Floral Whorls Research Articles

HISTOGENESIS OF THE ANDROECIUM AND GYNOECIUM IN DOWNINGIA BACIGALUPII

A histogenetic investigation of the synandrous androecium and syncarpous gynoecium in the flower of Downingia bacigalupii Weiler (Campanulaceae; Lobelioideae) was undertaken for the purpose of comparing the modes of initiation, early growth and fusion in these floral whorls with that reported previously for the perianth in this species. Stamens are initiated as separate organs from the second tunica layer and underlying corpus regions of the concave floral meristem. Subsequent growth of stamens involves apical and intercalary growth in length and rudimentary marginal growth in breadth. Tissues of the four microsporangia originate from hypodermal sporangial initial cells and the filament is formed by intercalary growth at the base of the anther. Lateral fusion of stamens is ontogenetic and involves cuticular fusion of adjacent epidermal layers. The two emergent carpel primordia arise as crescentic organs by periclinal divisions in the second tunica layer and corpus zones. Carpel primordia also undergo apical and intercalary growth in length as well as extensive marginal growth in breadth. Radial growth in carpels is mediated by an adaxial meristem which shows its greatest concentration of activity at the carpel margins. Carpel fusion appears to be partially ontogenetic accompanied by zonal growth. Closure of the stylar canal is by the formation of a transmitting tissue derived from the protodermal layers of the adaxial carpel surfaces. A discoid nectary is initiated around the base of the style and formation of the inferior ovary is by intercalary growth of the base of the concave floral bud. The two parietal placentae originate as longitudinal outgrowths from the walls of the floral cup. Ovule initiation is simultaneous at first and then intercalary during subsequent elongation of the ovary. The ovules are anatropous, unitegmic and tenuinucellate. Stamen and carpel procambium shows a slight delay in differentiation when compared to that reported for the perianth and bract, but in all other respects carpels resemble other floral organs in their patterns of histogenesis and early growth. Stamens diverge from the other floral organs in their early pattern of growth, but a consideration of all features of their histogenesis suggests an appendicular rather than an axial interpretation of these organs.

FLORAL MORPHOLOGY, ORGANOGENESIS AND INTERPRETATION OF THE INFERIOR OVARY IN DOWNINGIA BACIGALUPII

The inflorescence of Downingia bacigalupii (Campanulaceae; Lobelioideae) is an indeterminate spike. Axillary flowers have a long, linear, inferior ovary with parietal placentation, a pentamerous synsepalous calyx, zygomorphic sympetalous corolla, syngenesious stamens, and a bicarpellate, syncarpous gynoecium. On the basis of floral vascular anatomy the inferior ovary is interpreted as appendicular, representing adnation of outer floral whorls to the gynoecium. Floral ontogeny shows that sepals are initiated in an adaxial to abaxial sequence rather than the 2/5 phyllotaxis reported for other members of Lobelioideae. Growth of the common bases of sepal lobes forms a floral cup and initiation of the following floral whorls occurs along the inner margins of the cup. Continued basal growth of the cup‐shaped bud results in the formation of the elongated inferior ovary. Earlier evidence for the interpretation of a cup‐shaped receptacle during development of epigynous flowers is reexamined and it is concluded that the concave floral bud of D. bacigalupii can also be interpreted as common growth of connate floral whorls, supporting interpretations based on vascular anatomy. Comparison of floral development between Downingia bacigalupii and Pereskia aculeata (Cactaceae) reveals ontogenetic differences between flowers with appendicular and receptacular cups.

Floral Morphology, Organogenesis and Interpretation of the Inferior Ovary in Downingia Bacigalupii

The inflorescence of Downingia bacigalupii (Campanulaceae; Lobelioideae) is an indeterminate spike. Axillary flowers have a long, linear, inferior ovary with parietal placentation, a pentamerous synsepalous calyx, zygomorphic sympetalous corolla, syngenesious stamens, and a bicarpellate, syncarpous gynoecium. On the basis of floral vascular anatomy the inferior ovary is interpreted as appendicular, representing adnation of outer floral whorls to the gynoecium. Floral ontogeny shows that sepals are initiated in an adaxial to abaxial sequence rather than the 2/5 phyllotaxis reported for other members of Lobelioideae. Growth of the common bases of sepal lobes forms a floral cup and initiation of the following floral whorls occurs along the inner margins of the cup. Continued basal growth of the cup-shaped bud results in the formation of the elongated inferior ovary. Earlier evidence for the interpretation of a cup-shaped receptacle during development of epigynous flowers is reexamined and it is concluded that the concave floral bud of D. bacigalupii can also be interpreted as common growth of connate floral whorls, supporting interpretations based on vascular anatomy. Comparison of floral development between Downingia bacigalupii and Pereskia aculeata (Cactaceae) reveals ontogenetic differences between flowers with appendicular and receptacular cups.

STUDIES IN THE FLORAL MORPHOLOGY OF THE MARANTACEAE: I. VASCULAR ANATOMY OF THE FLOWER OF SCHUMANNIANTHUS VIRGATUS ROLFE, WITH SPECIAL REFERENCE TO THE LABELLUM

The floral anatomy of Schumannianthus virgatus Rolfe is described in detail. Anatomical observations indicate fusion of vascular bundles of various floral whorls commensurate with their adnation, and, in that sense, the inferior ovary is considered to be appendicular in nature. Anatomical evidence demonstrates reduction in part of the labellum and of the functional stamen. The anther is one-celled. The labellum is shown to be a unitary organ representing an anterolateral member of the inner androecial whorl.

The floral anatomy ofKaempferia rosea Schweinf. ex Benth. with special reference to the glands in zingiberaceae

The floral anatomy ofKaempferia rosea is studied in detail. Anatomical observations demonstrate fusion of vascular strands of different floral whorls. The inferior ovary is considered to be a result of extreme degrees of adnation.

The Floral Morphology of Clethra alnifolia with some Notes on C. acuminata and C. arborea. Contributions from the Hull Botanical Laboratory 632

1. Descriptions of the organography, floral development, vascular anatomy of the flower, anatomy of the floral organs, microsporogenesis, and megasporogenesis in Clethra alnifolia and notes on the organography, vascular anatomy, and anatomy of floral organs in C. acuminata and C. arborea are presented. 2. The Clethraceae, in common with most of the Ericales, are pentacyclic (the outer whorl of stamens opposite the petals), pentamerous in most floral whorls, actinomorphic, hypogynous, and hermaphroditic. Characteristics peculiar to the family are a fully developed endothecium in the anther and a three-branched style. Other features found in the Clethraceae and in only a few other species in the Ericales are choripetaly, absence of a disk, "stellate" pubescence, extrorse position of the anthers during development, single pollen grains, and a tricarpellate ovary. 3. In the receptacle the vascular cylinder is considerably compacted in the region where the traces originate. The first whorl, consisting of five bundles, forms the median sepal supply. The lateral traces of adjacent sepals arise as common bundles from the large strands of vascular tissue left between the median sepal gaps. Immediately above these common bundles the traces to the petals and petalad stamens arise together. Traces to the sepalad stamens arise from one side of the median sepal gap as do also the dorsal carpel bundles. The latter form the stylar vascular supply; the septal traces, independent in origin, fade out without reaching the style, and the ventral carpel bundles supply the placentae and ovules. 4. Inversion of the extrorsely developed anther occurs at anthesis. The pattern of microsporogenesis is as in most angiosperms. Pollen grains are single and probably two celled at the time of shedding. 5. In the ovule a single archesporial cell gives rise to the megaspore mother cell which, following meiosis, divides to form a linear tetrad. Usually the chalazal spore functions. The seven-celled, eight-nucleate, megagametophyte develops according to the Normal-(Polygonum-) type. Disintegration of the nucellus and development of an "epithelial"-like layer of the single integument begins prior to gametophyte development. Fusion of the polar nuclei occurs before fertilization. 6. C. acuminata and, to a lesser extent, C. arborea differ from C. alnifolia in the vascular supply of the sepals. Some variation in the type of pubescence occurs in C. acuminata as compared with the two other species. In C. arborea branches of the ventral carpel bundles as well as of the dorsal carpel bundles traverse the style. 7. A comparison of the characteristics of the Clethraceae, as exemplified by the three species studied, with those of other groups in the Ericales shows that the family is not so primitive with respect to the vascular anatomy of the flower as it is with respect to certain of its other morphological features. 8. Drude's separation of the three species studied into two sections appears to be justifiable on the basis of organography. Observed anatomical variations in the three species, however, neither support nor refute his classification.

Studies in the Capparidaceae.-II. Floral anatomy and some structural features of the Capparidaceous flower.*

SUMMARY. The paper deals with the floral structure of several genera and species of the Capparidaceae. The findings may be summarized as follows:— The prevalence of andromonoecism is recorded in Gynandropsis pentaphylla DC. The occurrence of what look like tricarpellary and tetracarpellary gynoecia in the species is explained and interpreted on the bicarpellary basis. The median sepals are found to be the lowest floral members; thus they occupy the position which would be expected had bracteoles been present; this view is supported by the actual occurrence of bracteoles in Euadenia eminens Hook. fil. and Capparis flexuosa Blume, and the belief that the Capparidaceae are bracteoleless is not accepted. The vasculation of the members of the different floral whorls in all stages of development has been traced. The ontogeny of the gynoecium shows that it is formed by the marginal fusion of two inrolled carpellary leaves. The foliar concept of the carpels is supported by anatomical evidence, the vasculation of the carpels being essentially that of a lateral organ, leaf or leaf-like appendage. The polymorphic carpel theory is discussed in the light of the present findings, and the conclusion is reached that it is not applicable to the Capparidaceae. In conclusion, it is a source of sincere pleasure for me to record my grateful thanks to Professor R. Ruggles Gates for his unfailing interest in the progress of the work and for much helpful guidance.

I.—A Study of the Vascular Supply to the Carpels in the Follicle-bearing Ranunculaceæ

In 1790 Goethe (Eng. Trans., 1863) published his doctrine of metamorphosis. Before that only two authors had expressed any fundamental ideas with regard to the flower. Wolff in his Theoria Generationis (1759) said that the plant consisted of nothing but stem and leaf, the root being a modification of the former; parts of the flower were appendages, and the production of floral leaves was due to degeneration of the sap, the richest portion being used up at a lower level by the vigorous first-formed foliage leaves.Linné (1760) expressed the same idea as Wolff, partly basing his evidence on teratological specimens, in which the various floral organs were sometimes found to be replaced by leaves. He further considered the flower to be a modified shoot, five years' growth being compressed into a single year. Believing that the different floral whorls were developed the one from the other, and observing that they encircled each other, he attributed the various floral envelopes to different tissues of the stem—e.g. the bark gave rise to the calyx, and the carpels arose from the pith.

The “Outside-In” Oenothera Flower, a New Morphological Type Produced by the Interaction of Two Recessive Mendelian Factors

The outside-in Oenothera flower is a new morphological structure of such intrinsic interest, and the method of its origin as the result of the interaction of two previously known recessive Mendelian genes so unique, that it seems worthwhile to publish a preliminary account instead of waiting for the development of the further genetical experiments which have been undertaken with it. The characteristic feature of the outside-in flower is the rhythmic repetition of three of the four sets of floral organs which make up the normal flower, so that the order of succession of parts as we pass from outside inward is: calyx, corolla, androecium, calyx, corolla, androecium, calyx, corolla, and so on. In some flowers as many as four repetitions of these floral organs have been recognized and no structures were found which could be identified as of carpellary nature, the ovary and hypanthium being replaced by a solid pedicel. Functional stamens were usually found only in the external one or two repetends. The more internal repetends have the stamens reduced to functionless staminodia, or even to structures whose identity cannot be determined. The recognition of the several floral whorls was rendered easier by the simultaneous presence of the rubricalyx factor, so that each repetition of the calyx could be recognized by the red pigmentation as well as by its texture and relative position with reference to other parts. It was this conspicuous presence in the interior of the flower of the red coloration normally seen only on the external surface of the calyx that led to the name outside-in for this type of flower. The outside-in flowers were first seen in the summer of 1926 in several individuals of an F2 family (No. 25115) from a cross between a doubleflowered old-gold Lamarckiana mother (SSvspQspBrBr) and a single-

A Contribution to the Life History of Apocynum androsaemifolium

IT appears that not one of the Apocynaceae, a family of about iooo species, has ever been studied carefully in reference to the minute morphology of the flower. Considering this in connection with the fact that the family stands near the Asclepiadaceae, with their peculiar pollen and stigma, it was believed that it deserved investigation. Buds and flowers of Apocynum androsaernijolium L. were collected in various stages, and the results of their investigation are herewith described. The order of appearance of the floral whorls is centripetal. The calyx shows no peculiarities other than a ruffling of the epidermis on the abaxial surface near the base, suggesting a mechanism for the folding of the sepals. Each petal of the campanulate corolla has on its inner surface near the base a ridge (fig. i, r) running from the midrib diagonally outward and toward its base. It is highest at the midrib, and undoubtedly functions as an aid in compelling cross-pollination. The ridge arises from the more superficial cells of the leaf, and does not affect the course of the veins. Its meristematic crest forms the cells for its enlargement. The stamens are peculiar in form, adjusting themselves neatly in a ring rather closely applied to the stigmatic head (fig. i, s). At the base of each are two long auriculate appendages (figs. I, 2, 3, ap) extending downwards dorsal to the filament. The sporangia are above the insertion of the filament, and do not extend into the appendages. The loculi open on their inner surfaces, somewhat laterally, by longitudinal slits, and immediately beneath them is a beard of epidermal hairs extending transversely across the faces of the anthers, forming a ring around the stigmatic head (figs. I, 2, b). These hairs meet similar ones from a ring around the head, thus preventing pollen from rolling into the base of the flower.

Book Reviews

IT is notorious that examinations in elementary practical chemistry are frequently little more than tests of capacity for remembering analytical tables. This little book will serve the same purpose in botany that tables of analysis do in chemistry. In thirty-four pages the authors summarise the work required for the South Kensington (Elementary) and the Oxford and Cambridge Junior Local Examinations in Botany. Charts and definitions are given of sub-kingdoms,classes,orders,and floral whorls; of root, stem, leaf, inflorescence, and fruit. These,.with definitions of terms of cohesion and adhesion, enable the student to classify a plant' on the lines of the table of analysis with which the book concludes. We are afraid that the compilation will induce cramming for the examinations for which it is intended; but if this be avoided, and the charts are only used as supplementary to oral teaching and demonstration, they will help students to acquire a clear view of the relation and arrangement of the parts of a plant.

Book Reviews

ON turning over the pages of this book one wonders why “Naked-Eye Botany” was chosen for the title, because, although a small book, it has some reference at least to a great many things that cannot be seen with the naked eye. It is something in the way of Prof. D. Oliver's “Lessons in Elementary Botany,” but one misses the Professor in it. On p. 7 we are introduced to stomata, and physiological processes are described in some detail. Nevertheless it contains much useful matter, and with a little revision and better selections would make a very good first book. For example, the chickweed is chosen for the first lesson. But the flowers of this plant are so. small and the number of parts in the various floral whorls is so variable that it is not a good subject to begin with. The “problems,” or questions, also at the end of each chapter are too wide-reaching. Referring to Aspidium Filix-mas, we are told that the “production of the fertilized seed, more correctly called oosphere, from the prothallus, can scarcely be made out with the naked eye.” Saying nothing about the name given to the fertilized body, we must protest that “scarcely” is not the word to qualify the observation.

Scientific Serials

IN the Botanical Gazette for February and March, Miss Alice Carter has an interesting paper on evolution in methods of pollination. She points out that the larger proportion of Monocotyledons are either anemophilous or hydrophilous, and this is undoubtedly an earlier method of pollination than the entomophilous. Of the twenty-three natural orders which comprise more than 1000 species, only five are characterized by inconspicuous flowers. Of these, four, viz. the Cyperaceæ, Gramineæ, Urticaceæ, and Piperaceæ, are probably ancestral types, the fifth, Euphorbiaceæ, degenerate. It is probable that the period of the appearance of Dicotyledons was also that of the development of our great groups of insects. The first step towards the attraction of insects was probably the colouring of the stamens, as in Thalictrum and Plantago; then the development and colouring of the corolla, and the production of saccharine secretions. The most highly developed orders appear to be those in which the number of parts in a floral whorl is small, as the Violaceæ, Compositæ, Labiatæ, and Scrophulariaceæ.—Mr. P. H. Rolfs has an article on the Seed-coats of Malvaceæ; and Mr. Chas. Robertson continues his researches on Flowers and insects.