Determinate Inflorescence Research Articles

Cytogenetic and morphological characteristics of new types of diploids (2n=22, 24, 40) derived from consecutive selfing of aneuploids in brassica crops

New types of diploids in Brassica crops were synthesized after three consecutive selfing of aneuploids derived from backcrossing of sesquidiploids (2n=29, AAC) with B. campestris (2n=20, AA). The cytogenetic and morphological characteristics of plants with 2n=22, 24 and 40 in the S3 generation were analyzed in order to establish the extent in which these addition and polyploid lines were stabilized. A high frequency of 11II (79.7%), 12II (84.6%) and 20II (100%), were observed at metaphase I of pollen mother cells in 2n=22, 24 and 40 plants, respectively. The chromosome configuration at methaphase II also indicates that a certain level of stability has been attained cytogenetically. Although pollen stainability was relatively high, the seed set percentage was still low. Variation in morphological characteristics indicate the incorporation of one or more chromosome pairs from the C genome of B. oleracea. Other diagnostic characters such as the formation of determinate inflorescence, branching from the base of the stem, and the shift from self-incompatibility to self-compatibility must have resulted from the interaction between A and C genomes. Thus plants with 2n=22, 24 and 40 have been stabilized to some extent and can be developed into new breeding lines of Brassica. It is suggested that limited pollination could be effective in increasing the seed fertility of these plants.

Plant Morphology and Anatomy in the Tropics-The Need for Integrated Approaches

Plant morphology, like justice, must not only be done, it must be seen to be done. It must be done because it is foundational to many major disciplinessystematics, ecology, and plant physiology. Similarly plant morphology is initially an observational discipline; the pun is intentional because I want to speak from the point of view of the research worker who needs direct access to his material and the opportunity to see the functional significance of form and structure which is investigated. Modern high speed travel has made easy the traditional process of what may be called body-snatching, i.e., the initial collection of fluid-preserved or dried materials which the plant morphologist uses for much of his work. Body-snatching has contributed the largest part to our understanding of tropical plants and needs to be actively encouraged because it provides the initial comparative background to any biological enquiry. Here I want to emphasize the need for elaboration of or departure from this classical approach in what I will call integrated studies of biological features of tropical plants. Integration here has a dual meaning, it refers to the need to combine elements of disparate disciplinesanatomy, physiology, biochemistry, ecology, and plant-animal interactions-but also emphasizes an approach which recognizes the organism itself as an integrated entity so that something of its total biology is revealed. Corypha provides a simple but dramatic example of a tropical plant consisting of a single hapaxanthic module in which the switch from vegetative to sexual growth is complete, with marked contrast between the massive unbranched vegetative axis to the highly branched determinate inflorescence, with resulting proliferation of another generation of meristems. Here vegetative and reproductive phases are sharply segregated, but they must occur in the right sequence and at the right time. A striking example, which illustrates the way in which a branched organism can function as an integrated physiological unit is provided by Cerberiopsis candelabrum (Apocynaceae), a small tree in New Caledonia which is monocarpic (Veillon, 1971). Here a tree that is architecturally precisely branched in the initial vegetative stage eventually shows synchronous flowering and fruiting which ends in itsdeath-rather like many annual weeds. A second species, C. comptonii, a treelet with smaller leaves, is not monocarpic. This genus therefore provides material for the study of a biological problem which may be approached comparatively but requires access to field populations. The plants under consideration are large and can only be represented in herbaria by fragments. An appreciation of the adaptive significance of this life style would draw on several disciplines-anatomy, physiology, and reproductive biology. It has to be appreciated that modern travel in the tropics is easy and a

Spiral Developmental Patterns in the Stem and Inflorescence of Lilium tigrinum

Extensive correlations in spirality were observed among vegetative and floral organs in Lilium tigrinum Ker. Organs involved were vegetative leaves, bracts, and bracteoles. These correlations varied in their degree of constancy depending upon the organs involved. The mature inflorescences of L. tigrinum appeared to fit the common definition of a raceme. In 67.3% of the flowers at node 3 on the raceme, the bract-bracteole spirals reversed the spiral of vegetative leaves on the stem. These reversals resembled those observed on essentially cymose inflorescences of certain members of the Caryophyllaceae. Cymose branching was found to be an invariable feature of the inflorescence of L. tigrinum when secondary flowers appear. The apparently indeterminate tips of inflorescence main axes were interpreted as exhibiting stages in progression from a basically determinate (cymose) inflorescence. It was concluded that the ancestors of L. tigrinum had well-developed cymose branching patterns in the inflorescence. Reversal of stem spirals by the bract-bracteole spirals at the apices of many inflorescences was considered to be the result of complete utilization of the inflorescence meristem. Explanations for those reversals were provided by the field theory and by the theory of the first available space.

SPIRAL DEVELOPMENTAL PATTERNS IN THE STEM AND INFLORESCENCE OF LILIUM TIGRINUM

Extensive correlations in spirality were observed among vegetative and floral organs in Lilium tigrinum Ker. Organs involved were vegetative leaves, bracts, and bracteoles. These correlations varied in their degree of constancy depending upon the organs involved. The mature inflorescences of L. tigrinum appeared to fit the common definition of a raceme. In 67.3% of the flowers at node 3 on the raceme, the bract‐bracteole spirals reversed the spiral of vegetative leaves on the stem. These reversals resembled those observed on essentially cymose inflorescences of certain members of the Caryophyllaceae. Cymose branching was found to be an invariable feature of the inflorescence of L. tigrinum when secondary flowers appear. The apparently indeterminate tips of inflorescence main axes were interpreted as exhibiting stages in progression from a basically determinate (cymose) inflorescence. It was concluded that the ancestors of L. tigrinum had well‐developed cymose branching patterns in the inflorescence. Reversal of stem spirals by the bract‐bracteole spirals at the apices of many inflorescences was considered to be the result of complete utilization of the inflorescence meristem. Explanations for those reversals were provided by the field theory and by the theory of the first available space.