Initiation Of Leaf Primordia Research Articles

Localized upregulation of a new expansin gene predicts the site of leaf formation in the tomato meristem.

Expansins are extracellular proteins that increase plant cell wall extensibility in vitro and are thought to be involved in cell expansion. We showed in a previous study that administration of an exogenous expansin protein can trigger the initiation of leaflike structures on the shoot apical meristem of tomato. Here, we studied the expression patterns of two tomato expansin genes, LeExp2 and LeExp18. LeExp2 is preferentially expressed in expanding tissues, whereas LeExp18 is expressed preferentially in tissues with meristematic activity. In situ hybridization experiments showed that LeExp18 expression is elevated in a group of cells, called I1, which is the site of incipient leaf primordium initiation. Thus, LeExp18 expression is a molecular marker for leaf initiation, predicting the site of primordium formation at a time before histological changes can be detected. We propose a model for the regulation of phyllotaxis that postulates a crucial role for expansin in leaf primordium initiation.

Leaf primordia initiation, leaf emergence and tillering in wheat (Triticum aestivum L.) grown under low phosphorus conditions.

In two simultaneous experiments we examined the effects of phosphorus (P) supply on leaf area development in wheat (Triticum aestivum L.) grown in sand with nutrient solutions. In Experiment 1 we studied leaf emergence, leaf elongation, tiller emergence, shoot growth, and P uptake under four levels of P supply (mM) 0.025 (P1), 0.05 (P2), 0.1 (P3), and 0.5 (P4), and. In Experiment 2 there were two levels of P supply, P1 and P4, and we examined the effects of P on leaf primordia differentiation and leaf emergence. The phyllochron was calculated as the inverse of the rate of leaf emergence calculated from the regression of number of leaf tips (PHY-Ltip), Haun index (PHY-Haun), and as the cumulated thermal time between the emergence of two consecutive leaves (PHYtt). The plastochron was calculated from the inverse of the rate of leaf primordia initiation in the apex. P deficiency delayed the emergence of leaves on the main stem and on the tiller 1. Phosphorus deficiency increased the time from emergence to double ridge and anthesis. The final number of leaves was not affected by P. The effects of P on the value of the phyllochron were attributed to both a reduced rate of leaf primordia initiation, and to a reduced leaf elongation rate. P deficiency delayed or even suppressed the emergence of certain tillers. In this work a phosphorus deficiency that reduced shoot growth by 25% at 44 days after emergence significantly modified the structure of the plants by increasing the value of the phyllochron and delaying tillering. These results suggest that any attempt to simulate leaf area development and growth of wheat plants for P-limited conditions should include the effects of the deficiency on leaf emergence.

Comparative study of the development of zygotic and somatic embryos of chickpea ( Cicer arietinum L.)

The early stages of development of zygotic and somatic embryos (globular, heart and early cotyledonary stage) were studied in chickpea ( Cicer arietinum L.). Immature pods were collected 3–15 days after pollination (DAP) and used for the isolation of zygotic embryos. Immature cotyledonary segments and mature embryo axes of cultivar PG12 were cultured on Murashige and Skoog's (MS) basal medium supplemented with 3.0 mg l −1 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), for the induction of somatic embryos. The suspensor of zygotic embryo of chickpea was found to consist of six tiers of biseriate cells. By contrast somatic embryos were raised on a multiseriate suspensor-like stalk. The size of a globular-stage somatic embryo was much larger than zygotic embryo at a similar stage of development. The initiation of leaf primordia from the shoot apical meristem was also studied. The cells that composed the apical dome differed, in that the cells of zygotic embryo were flat in comparison to the curved cells of somatic embryo. Germinated seedlings and converted somatic embryo showed similarity in organization, differing only in the size of cotyledons.

Leaf Primordium Initiation and Expanded Leaf Production are Co-ordinated through Similar Response to Air Temperature in Pea (Pisum sativumL.)

Accurate prediction of the timing of leaf area development is essential to analyse and predict the responses of crops to the environment. In this paper, we analyse the two processes determining the chronology of leaf development—initiation of leaf primordia by the shoot meristem and production of expanded leaves out of the shoot tip—in several pea (Pisum sativumL.) cultivars in response to air temperature and plant growth rate. Contrasting levels of air temperature and plant growth rate during leaf development were induced by a wide range of sowing dates and plant densities in glasshouse or field experiments. Full leaf expansion was found to occur one phyllochron after full leaf unfolding, whatever the leaf nodal position. Primordium initiation and expanded leaf production rates presented similar quantitative responses to air temperature (linear response and commonx-intercept), whatever the plant growth rate, cultivar or period of cycle. As a consequence, they were co-ordinated and the numbers of initiated primordia or expanded leaves were easily deduced from simple visual observation of leaf unfolding. The change, over time, of the numbers of initiated leaf primordia and fully expanded leaves correlated with cumulated degree-days, with stable relationships in a wide range of environmental conditions. Two phases, with different production rates, had to be considered. These results allowed us to predict accurately the beginning and the end of individual leaf development from daily mean air temperatures. The relationships obtained here provide an effective way of analysing and predicting leaf development responses to the environment.

Free‐Air CO2 Enrichment Effects on Rate and Duration of Apical Development of Spring Wheat

Rates and durations of individual phases of wheat (Triticum aestivum L.) apical development are among the most important factors that determine yield components. Because atmospheric CO2 has been increasing steadily, it is important to evaluate the effects of elevated CO2 on wheat development. This study was conducted to determine rates and durations of leaf, spikelet, and floret primordium initiation in a Free‐Air Carbon Dioxide Enrichment (FACE) system. Spring wheat (cv. Yecora Roja) was planted at the University of Arizona Maricopa Agricultural Center. The two CO2 concentrations were 550 (elevated) and 370 (ambient) μmol mol−1 CO2. Individual plant samples were collected every 3 to 4 d. We dissected the main stem (MS), coleoptile tiller (T0), primary tillers (T1, T2, and T3) and secondary tillers (T00, T01, T02, T10, Tll, and T12) and counted primordia. Apex primordium data were fitted to a four‐piece linear‐spline segmented regression model with the SAS proc NLIN. No influence of elevated CO2 (550 μmol−1 on leaf primordium initiation of MS was detected. Nevertheless, CO2 enrichment significantly increased rates of spikelet primordium initiation of MS, T1, T2, T10, and Tll, and diminished the durations of spikelet development phase of MS, TI, T2, T3, T10, and T11. Within the floret phase, CO2 enrichment significantly increased rates of floret primordium initiation of MS, TO, T1, T2, and T3, and diminished the time to the completion of floret primordium initiation of MS, T0, T1, T3, and T11. The information from this study will be utilized to predict wheat apical development and grain production in the elevated atmospheric CO2 environments of the future.

Relationship between annual cycle and floral development of threeAlliumspecies from subgenusMelanocrommyum

Scanning electron microscopy (SEM) was used to study the monocarpic shoot development and florogenesis of three species from the genusAllium, in connection with their annual cycle. Initiation of leaf primordia in the Central Asian species,A. karatavienseandA. altissimum, begins with the renewal bulb during the flowering stage of the mother plant. After differentiation of leaf primordia, the apical meristem of these species remains inactive for 6–10 weeks. The meristem begins florogenesis in August, during the ‘dormancy’ stage of the mother plant. InA. rothiifrom the Negev desert, the apical meristem remains inactive for 12–15 weeks after flowering of the mother plant, leaf primordia form in July–October and the meristem then becomes reproductive immediately. Since the inflorescences of all the species studied consist of regularly arranged cymes, many stages of floral development can be observed simultaneously.

Temperature Response of Vernalization in Wheat: A Developmental Analysis

The vernalization response of wheat ( Triticum aestivumL.) was reinterpreted from a developmental perspective, using current concepts of the developmental regulation of wheat morphology and phenology. At temperatures above 0 °C, the effects of the process of vernalization per sein wheat are confounded by the effects of concurrent vegetative development. These effects are manifested by differences in the number of leaves initiated by the shoot apex prior to floral initiation, which in turn affects the subsequent rate of development to ear emergence and anthesis. Leaf primordia development during vernalization and total leaf number at flowering were used to develop criteria to define both the progress and the point of saturation of the vernalization response. These criteria were then used to reinterpret the results of Chujo ( Proceedings of the Crop Science Society of Japan 35: 177–186, 1966), and derive the temperature response of vernalization per sefor plants grown under saturating long day conditions. The rate of vernalization increased linearly with temperature between 1 and 11 °C, such that the time taken to saturate the vernalization response decreased from 70 d at 1 °C to 40 d at 11 °C. The rate declined again at temperatures above 11 °C, and 18 °C was apparently ineffective for vernalization. Total leaf number at saturation, however, increased consistently with temperature, as a result of the balance between the concurrent processes of leaf primordium initiation and vernalization. Total leaf number at saturation increased from 6 at 1 °C to 13.3 at 15 °C, which in turn influenced the time taken to reach ear emergence. The advantages of using this developmental interpretation of vernalization as the basis for a mechanistic model of the vernalization response in wheat are discussed.

Temperature Response of Vernalization in Wheat: Modelling the Effect on the Final Number of Mainstem Leaves

This paper outlines a modelling approach which predicts the effect of both continuous and intermittent low temperature regimes on the final number of leaves in winter wheat. The model takes account of the balance between the concurrent processes of leaf primordium initiation and rate of saturation of vernalization, and their response to temperature. The inverse of the time to saturation of vernalization, at which stage final leaf number is set, is modelled as a linear function of vernalizing temperature, between 0 and 17 °C. The rate of leaf primordium initiation is modelled using the established linear relationship between rate and temperature above 0 °C. Final leaf number is hence the product of the number of leaf primordia initiated once vernalization is saturated. In the model, genotypes are characterized by (1) the slope and intercept of the linear response of the rate of saturation of vernalization to temperature in the vernalizing range, and (2) by a development rate towards floral transition at on-vernalizing temperatures (above 17 °C). The model is tested against data from experiments where six cultivars of winter wheat plants of different ages were exposed to a range of low temperature regimes, including continuous and intermittent vernalizing temperatures. Overall, the model predicted, with r 2values of 70–90%, the final leaf number across a range of six to 21 leaves. Prediction of final leaf number for some cultivars was better in continuous than in intermittent vernalizing regimes. This modelling approach can explain the often-conflicting reports of the effectiveness of different temperatures for vernalization, and the interaction of plant age and vernalization effectiveness.

The Acceleration of Primordium Initiation as a Component of Floral Evocation in Lolium temulentum L

An acceleration of leaf primordium initiation by the shoot apex frequently follows floral evocation, but after varying intervals. The purpose of the experiments reported here was to define more closely the relation between this reduction of the plastochron and floral evocation, using the long day (LD) plant Lolium temulentum grown under closely controlled conditions.The acceleration begins at floral evocation, on the day after the first LD exposure, and increases after exposure to additional LDs. However, plants too young to be florally evoked by one LD nevertheless manifested an acceleration of primordium initiation, so the acceleration alone is not sufficient for evocation. Single applications of highly florigenic gibberellins (GAs), such as GA5, also accelerate the initiation of primordia and floral development, more so than does the weakly florigenic GA1. By contrast, single applications of the growth retardant Trinexapac-ethyl (CGA 163'935) to plants given one LD largely prevented the acceleration of primordium initiation but without inhibiting floral development. Thus, although the acceleration of primordium initiation by LD or by GA application is the first external sign of floral evocation in L. temulentum, it is neither a sufficient nor an essential component of it.

Elevated CO2 and plant growth: cellular mechanisms and responses of whole plants

Abstract Much research has focused on the photosynthetic responses of plants to elevated CO2 , with less attention given to the post-photosynthetic events which may lead to changes in the growth of tissues, organs and whole plants. The aim of this review is to identify how plant growth is altered in elevated CO2 and to determine which growth processes or cellular mechanisms are sensitive to carbon supply. For leaves, both the expansion of individual leaves and the initiation of leaf primordia are stimulated in elevated CO2. When lamina growth is promoted, this is usually associated with increased leaf cell expansion rather than increased leaf cell production. Using several clones of hybrid poplar (Populus euramericana, P. interamericana) two native herbs (Plantago media, Sanguisorba minor) and bean (Phaseolus vulgaris) we have identified the mechanism through which leaf cell expansion is promoted in elevated CO2. Changes in the water relations, turgor pressure (P) and yield turgor (Y) of growing leaves cannot explain increased cell expansion; this appears to occur because cell wall loosening is promoted, as suggested by three pieces of evidence. (i) The rate of decline of water potential (ψ) with time is accelerated when growing leaves are placed in psychrometers and allowed to relax, (ii) Instron-measured cell wall extensibility (WEX), is greater for leaves exposed to elevated CO2 and (iii) the activity of the putative wall loosening enzyme, XET is increased for leaves of P. vulgaris exposed to elevated CO2. Species differences do, however, exist; in the herb Lotus corniculatus small stimulations of leaf growth in elevated CO2 are due to increased leaf cell production and decreased cell size in elevated CO2. These results are discussed in relation to the concept of functional types. There is evidence to suggest that both cell production and cell expansion are promoted in roots of plants exposed to elevated CO2. For native herbs (Anthyllis vulneraria, Lotus corniculatus, P. media and S. minor), increased root growth in elevated CO2 is due to increased cell elongation. In contrast to leaves, this appears to occur because both root cell turgor pressure (P) and root cell wall extensibility (WEX) are promoted by exposure of shoots to elevated CO2. In longer-term studies on root growth, the effects of additional carbon on the production of root primordia and root branching are of overriding importance, suggesting that carbon supply may influence some aspect of the cell cycle, when effects on the extension of individual roots may not be apparent.

Flowering in celeriac ( Apium graveolens L. var. rapaceum (Mill.) DC.): effects of photoperiod

The role of photoperiod in time of flowering in celeriac ( Apium graveolens L. var. rapaceum (Mill.) DC.) was analysed for three different phases, namely thermoinduction, evocation and inflorescence development. The effect of photoperiod during thermoinduction on the relationship between duration of exposure to a low temperature and the progress of thermoinduction was studied by transferring plants at different times from 12°C with a photoperiod of 8 or 16 h, to 20°C. The degree of thermoinduction at the time of the transfer was determined by later counting the final number of leaves. The degree of thermoinduction at 8 and 16 h did not increase during the first 21 days of the low temperature treatment, but it increased linearly after 21 days until thermoinduction was completed after 39 (8 h) and 34 (16 h) days. Rate of initiation of leaf primordia on the apex decreased with increasing photoperiod from 0.65 leaves per day at 8 h to 0.47 leaves per day at 16 h. At a photoperiod of 8 h completion of thermoinduction was followed immediately by initiation of the primordia of the main umbel on the apex. However, if plants remained at 16 h after the completion of the thermoinduction, leaf primordium initiation on the apex was strongly retarded, and initiation of the final leaf was delayed. If the photoperiod was varied after initiation of the main umbel on the apex, time of flowering of the main umbel at a photoperiod of 24 h was approximately 8 days earlier than at a photoperiod of 10 h. The main inflorescence stalk developed only at a 24 h photoperiod; at 10 h the main umbel was directly implanted on the tuber.

951 PB 446 RESPONSE OF TOMATOES GROWN IN AN AEROPONIC GROWTH CHAMBER

An aeroponic growth chamber is a system for growing plants in air with water and nutrients supplied by intermittent mist. This type of plant growth system is especially useful for experiments where root accessibility is desired. Tomatoes (Lycopersicon esculentum L. `Bonnie Best') were used to test the performance of an aeroponic growth chamber. A nutrient solution mist was applied through spray nozzles suspended below roots of supported seedlings. Mist application was regulated by electric timers, so that mist was applied for 50 sec. every 5 min. during the 16-hr light period, which was supplemented with a high-pressure sodium lamp. Root and stem lengths, leaf number and leaf lengths were measured weekly. Plastochron index (PI) was used to measure rate of leaf initiation. PI increased linearly, indicating uniform initiation of leaf primordia and absence of environmental stresses. Stem and root lengths increased consistently throughout the growing period. Each plant was harvested, separated into leaves, shoots and roots, oven dried, and dry weights measured.

Leaf and Spikelet Primordia Initiation in Salt‐Stressed Wheat

Salt stress is known to affect adversely shoot apex development in cereals. This study was conducted to determine rate and duration of leaf and spikelet primordia initiation as related to final leaf and spikelet numbers in salt‐stressed wheat (Triticum oestivum L.). Early shoot development of two hard red spring wheat cultivars, Yecora Rojo and Anza, was studied in both greenhouse sand cultures and outdoor field lysimeters. In each case, two saline treatments were compared with a nonsaline control treatment. The sand cultures were irrigated with complete nutrient solutions to which NaCI and CaCI2 (2:1 molar ratio) were added to achieve electrical conductivities (K1W) of 1.7, 12.2, and 15.1 dS m−1. Lysimeters were irrigated with tap water salinized to KlW levels of 0.8, 11.4, and 17.1 dS m−1. Timing of primordium initiation was expressed in accumulated thermal time measured in the soil (°C dsoil). A three‐piece linear‐spline model was developed to facilitate the statistical analysis and interpretation of primordium initiation. Parameters of the model corresponded to morphologically significant events. In both experimental locations, each genotype exhibited a similar response to increasing salinity. The rate of leaf primordium initiation decreased while the duration of this phase was unchanged. Salinity had no effect on the rate of spikelet primordium initiation of the genotypes, but the duration of this phase was shortened. As a result, the number of leaves on the main stem and the number of spikelets per spike were significantly reduced by salinity and the yield potential of both genotypes was severely limited.

Floral initiation, leaf initiation and leaf appearance in sunflower

This paper examines the hypothesis that leaf number visible at floral initiation (LN n) and final leaf number (FLN) are correlated in sunflower ( Helianthus annuus L.). The relationship between these variables is described by a model that takes into account the rate of leaf primordium initiation (RPI), the rate of leaf appearance (RLA) and time from emergence to floral initiation (FI). Data from glasshouse and field experiments were used to test the model. Combination of eight hybrids and four inbred lines and and wide range of growing conditions yielded values from 4 to 20 for LN n and from 12 to 42 for FLN. The observed relationship between LN n and FLN was in good agreement with the theoretical model. A constant RLA:RPI ratio underlies the association between LN n and FLN, and suggests that leaf initiation and appearance are co-ordinated processes. The relationship LN n and FLN is proposed as a non-destructive method to estimate the time of FL.

Comparative leaf development of conventional and semileafless peas (Pisum sativum)

Comparative leaf development of conventional (cv. Improved Laxton's Progress) and semileafless (cv. Curly) peas was studied three-dimensionally, from initiation to maturity. The pattern of initiation of leaf primordia, stipules, and the pairs of lateral leaflet and tendril primordia is the same for both cultivars. However, their respective developmental pathways diverge by the time four pairs of lateral primordia have formed. In the conventional cultivar, the basal lateral primordia become increasingly dorsiventral as they develop into leaflets. Distal lateral primordia retain a cylindrical form and develop into tendrils. In contrast, basal first-order lateral primordia of the semileafless cultivar retain a cylindrical form and initiate second-order primordia, first in pairs, then in an alternate pattern. These second-order primordia develop into tendrils. Distal lateral primordium initiation and development are the same in both cultivars. Macroscopic development was subdivided into three stages based on tendril function. Stage I is an elongation phase during which the coiling response is not yet exhibited. During stage II, the tendrils are thigmotropic and retain their capacity to elongate. By stage III the tendrils have completed coiling and they no longer respond to thigmotropic stimuli. Stage I lasts an average of 1.4 ± 0.1 days in 'Improved Laxton's Progress' and 2.1 ± 0.1 days in 'Curly' from emergence from the stipule. Stage II may last up to 8 days, with an average of 6.4 ± 0.2 and 6.9 ± 0.3 days for 'Improved Laxton's Progress' and 'Curly', respectively, under greenhouse conditions for both cultivars. Key words: peas, Pisum sativum, leaf development, tendrils, afila.

Pleiotropic effects of the GA-insensitive Rht dwarfing genes in wheat. 1. Effects on development of the ear, stem and leaves

Analysis of near-isogenic lines carrying Rht1, Rht2 or Rht3 in the genetic background of spring and winter wheat varieties showed that these dwarfing genes have no effects on the number of organs, or on the timing of developmental events. The characters studied included leaf and spikelet primordium initiation, leaf emergence and stem internode extension. The conclusion is reached that the genes do not directly affect developmental events, and that their effects on grain numbers and yield must be the result of an altered pattern of growth.

Leaf and flower initiation in potato (Solanum tuberosum) sprouts and stems in relation to number of nodes and tuber initiation

SUMMARYExperiments were conducted in controlled environment cabinets and in the field at Cambridge, UK, in 1987–90 and in Valencia, Spain 1989–90 with several varieties of potato. The initiation of leaf primordia and flowers was recorded in sprouts stored for long periods at 13°C with constant illumination and in sprouts exposed to different photoperiods and periods of cold storage. In field experiments, the effects of a wide range of planting dates, differences in physiological age, the time at which seed tubers were sprouted and of imposing an 8 h photoperiod were investigated.More than 40 leaf primordia were initiated in the sprouts of Home Guard and Arran Comet stored at 13 °C, but, in other varieties, fewer leaves were initiated. Flowers were initiated in the sprouts of some varieties. In field-grown plants, the number of nodes to the first flower differed between varieties and was increased by ageing sprouts before planting. Stems from physiologically old seed of all varieties had more nodes below ground than young seed but the number of aerial leaves to the first flower increased only slightly with increasing physiological age. The number of aerial leaves to the first flower was lower and less variable in Estima than in Maris Piper.Initiation of flowers usually occurred before tuber initiation and within two weeks of emergence but was earlier in some varieties than others. There was little influence of photoperiod on the time to initiation of flowers and tubers in most experiments but, with low levels of radiation, flowering was completely inhibited in the variety Maris Piper.

Co-ordination of leaf emergence and leaf and spikelet primordium initiation in wheat

Abstract Leaf emergence and primordium initiation were measured in experiments done with different varieties in a wide range of environments. Leaf initiation, relative to leaf emergence, proceeded at a constant rate. After initiation of the first spikelet, the rate of primodium initiation (primordia per emerged leaf) changed to a faster, approximately constant, rate which was maintained until initiation of the terminal spikelet. Rate of leaf initiation (1.7 primordia per emerged leaf) was similar in all cases analysed. Rate of spikelet initiation varied from about 3.5 to 7 primordia per emerged leaf, and was negatively correlated with total number of leaves on the shoot, which varied from 7 to 14. A rectangular hyperbola describes the relation between rate of spikelet initiation and total number of leaves. The analysis shows that there is a metrical relationship between different elements of shoot development. A model is given which shows how ear initiation and stem elongation are modulated in shoots with differing total numbers of leaves. The relation between leaf emergence and primordium initiation suggests control of apex development by emerging leaves, or vice versa. An accumulation of growing leaves may regulate growth and development of the shoot apex.

Early Leaf Ontogeny and Shoot Development in Brownea ariza (Leguminosae)

Brownea ariza Benth. (Leguminosae: Caesalpinioideae) shows early shoot tip abortion and subsequent renewal growth from the pseudoterminal bud. This species is unusual in that the entire shoot system is formed before flushing from the bud occurs, shoot tip abortion occurs during flushing, and the aborting portion contains three to six leaves as well as primordial structures varying from hood to peg shape. This study focused on the morphological changes from initiation of scale and foliage leaf primordia in the “resting” renewal bud through bud elongation to flushing and bud abortion. Scanning electron microscopy revealed that embryonic scale leaves are hood-shaped while foliage leaf primordia show early segmentation into leaflets and stipules. No transitional stages were observed. Bud scales and foliage leaves show opposite developmental trends. In bud scales, length at maturity increases from first to last formed, while length decreases in sequentially formed foliage leaves. Early in leaf development the stipules keep pace with the elongation of the rachis. When the bud reaches about one half of its final length the leaf rachis begins to exceed the lengths of its stipules. This young rachis terminates in a distinct mucro that persists until maturity at which time it abscises. Growth patterns indicate that mucro and rachis are a single developmental unit. The early abortion of a shoot tip containing several leaves cannot be easily rationalized. Previous suggestions have involved maintenance of form and ecological adaptation. We add the possibility of elimination of cell progeny encumbered by mutations. From this and other studies of this group, it is clear that at maturity leaves of different species may look alike, e.g., Hymenaea and Colophospermum are bifoliolate; Brownea, Saraca, and others are multifoliolate. However, early stages of leaf ontogeny are quite diverse and may be of systematic value, since these early differences are lost or masked by later development.

EARLY LEAF ONTOGENY AND SHOOT DEVELOPMENT IN BROWNEA ARIZA (LEGUMINOSAE)

Brownea ariza Benth. (Leguminosae: Caesalpinioideae) shows early shoot tip abortion and subsequent renewal growth from the pseudoterminal bud. This species is unusual in that the entire shoot system is formed before flushing from the bud occurs, shoot tip abortion occurs during flushing, and the aborting portion contains three to six leaves as well as primordial structures varying from hood to peg shape. This study focused on the morphological changes from initiation of scale and foliage leaf primordia in the “resting” renewal bud through bud elongation to flushing and bud abortion. Scanning electron microscopy revealed that embryonic scale leaves are hood‐shaped while foliage leaf primordia show early segmentation into leaflets and stipules. No transitional stages were observed. Bud scales and foliage leaves show opposite developmental trends. In bud scales, length at maturity increases from first to last formed, while length decreases in sequentially formed foliage leaves. Early in leaf development the stipules keep pace with the elongation of the rachis. When the bud reaches about one half of its final length the leaf rachis begins to exceed the lengths of its stipules. This young rachis terminates in a distinct mucro that persists until maturity at which time it abscises. Growth patterns indicate that mucro and rachis are a single developmental unit. The early abortion of a shoot tip containing several leaves cannot be easily rationalized. Previous suggestions have involved maintenance of form and ecological adaptation. We add the possibility of elimination of cell progeny encumbered by mutations. From this and other studies of this group, it is clear that at maturity leaves of different species may look alike, e.g., Hymenaea and Colophospermum are bifoliolate; Brownea, Saraca, and others are multifoliolate. However, early stages of leaf ontogeny are quite diverse and may be of systematic value, since these early differences are lost or masked by later development.