HARN. Chang Yawl (Chonnam U. Kwangju Korea) - Studies on the dimorpism and Transition of disexuality of keterostylous Polyonaceae- Kor. jour. Bot 3(2): 6-18 1960 The present experiments were designed in order to clarify the differences between the long and short styled plants and the transgresssive gradition in the degree of dimorphism among the three heterostylous species of the Polygonus, P. japonica, F. esculentum, and P. senticosa, based on investigations regarding the floral structure, ecological and physiological traits, the results of which are sunmarized as follows:
(1) P. japonica, although it exhibits typical dimorphism, has undergone so high a differentiation between long and short styled that its long styled individuals behave as if they were female; and short styled individuals as if male. In long-styled individuals, filament, anther, and pollen grains show signs of degeneration, most of the pollen being abortive. On the other hand, in short styled individuals, the filament, anther, and pollen grains have attained remarkable development; the pollen grains are large and fertile. In short-plant the fertilized flowers readily drop off in every stage of their embryo development. This species has completely lost the self-fertile property, which is characteristic of the non-dimorphic Polygonum genus. Althugh this specsei typically exhibits the physiological characteristics of dimorphism in controlled pollination, the short-styled individuals bear no seed in nature, thus misleading taxonomists to identify the short-styled plant as male.
2) The morphological feature of the flower organ of P. senticosa obviously indicates definite dimorphism. Physiologically, however, no differentiation towards dimorphism was observed, the specics stil retaining, both in long and shot-individuals, the self-fartile property common to the Polygonum genus. Elaborate examinations revealed that regardless of the modes of pollination, both felrtilization and seed setting flourish, no differentiation between legitimate and illegitimate unions being recognizable. This sort of physiologica1 property has not been observed in the investigations of other heterostylous plants. It is assumed that this species is differentiated structurally into dimorphism, but not yet physiologically. In nature, however, this plant would have more opportunities to be cross-pollinated, i. e., legitimately combined, than self-pollinated because of the development of two forms of flowers.
3) In terms of heterostylism, the F. esculentum just occupies the intermediate position between P. japonica and P. senticosa structurally, ecologically, and physiologically. Doescription of some of the physiological behavior of the plant will suffice to demonstrate the above fact. While P. japonica has completely lost its self-fertile property, P. senticosa still retains it wolly. In F. esculentum 2-6% of self-fertility is the result in illegitimate combination. There occur occasionally hereditary self fertile individuals among some of the F. esculentum. P. japonica have no such individuals. In P. senticosa since complete fertility is the result in iliegitimate combination, it may be said that in this species the occurrence of self-fertile individual is 100%.
4) P. japonica, by the extreme structural differentiation of flower forms, not only givs the impression of its transition toward dioecious, but physiologicalty it also indicates the sign that the long-style plays the role of pistil, and the short-style, the seamen. Contrary to this. P. senticosa has developed two forms of flowers, thus exhibiting dimorphic features, but no diferentiation has yet occurred physiologically, still retaining fully the original property of non-dimorphic Polygonum genus. F. esculentum takes the intermediate position morphologically, ecologically, and physiologically. If it is assumed that in these species the transition has taken place from harmaphrodite to dimorphism, P. japonica would be the most advanced type and the P. senticosa, the primitive type, and the F. escutentum, the transition type.
5) It is conceivable that Polygonum genus, originally homo-styled and self-fertile morphologically and functionally, developed a partial allogamous property through the formation of a nectary gland, and some of the species have attained the means of ensuring more cross-pollination through the development of dimorphism of flower form, and through alteration of the self-fertile property into a self-incompatible one. The degree of changes may vary in different species, with P. japonica attaining the most advance type, and P. senticosa, the least. Moreover, the changes which P. japonica has undergone are so great that in appearance it exhibits some of the characteristics of a dioecious plant. These facts lead to the possibility that another course of differentiation of sex in the sporophytic generation of higher plants may exist from hermaphrodite through heterostylism leading to dioecious.
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