General Part

Abstract

To start with the description of the structure and dispersal methods of the studied fruits and seeds we have to give first a general survey of the existing fruit and seed forms and types as well as of their possible dispersal strategies. In my book “Fruits of Angiosperms”(1977) I had the opportunity to present an exact definition of the fruit so that it seems sufficient here to draw attention to this bibliography. A classification of fruits on an evolutionary basis is likewise presented in the same text. In spite of our knowledge of fruit evolution which permits the performance of a phylo-genetic classification (presented on p. 5 1.c.) this can hardly be utilized for practical purposes. Consequently, we have to deal more or less with the old classification of dehiscent and indehiscent fruits. Within the indehiscent fruits we distinguish the nut with a hard pericarp and a single seed, the single-seeded drupe with a fleshy-stony pericarp, and the many-seeded berry with a fleshy pericarp. The aggregate fruit represents a special fruit type, as well as the compound infrutescence. During the phylogenetic development of the fruit a reduction of seeds may have taken place. We observe this process in the dehiscent as well as in the indehiscent fruits. A many-seeded capsule may become single-seeded in this way and even loose the ability to dehisce as a consequence of monospermy. It may transform in this way into a monospermic nut. The polyspermic indehiscent fruit with a hard or dry pericarp may undergo reduction of seeds during evolution and additionally develop a fleshy outer pericarp part so that it becomes a drupe. Even polyspermic berries may reduce their seed number to only one during evolutionary processes. However, nature never draws strict insuperable limits between forms, and transitional types may be found everywhere. Consequently, the distinction between a monospermic berry and a drupe is sometimes difficult. Furthermore, the hard endo-carp postulated for a drupe may not always be present in the desired form. I, therefore, suggest to use the term“drupe”for a fleshy single-seeded fruit in general. The reader will find many examples of seed reduction in fleshy fruits within the below cited families. One could possibly make a distinction between a syncarpic drupe with several stones (“pyrene”), and a drupe originating from a single carpel by seed reduction (“putamen”). Winged fruits called“samaras”and other wind-dispersed fruits with hairs of different kinds or with a persistent enlarged calyx or perigone are probably derived forms of the nut-type. This opinion coincides with our concept of the evolution of wind dispersal. In many families we find examples of secondary wing formation or even beginning wing development, e.g. within the papilionacean species Pterocarpus. Wind dispersal is often related to the height of the tree or the special environment of the species. Likewise other fruit types with stiff hairs, hooks, glands or similar devices have to be considered derived forms. Apocarpic fruits are certainly primitive and the follicle has undergone the same processes of reduction and transformation as the paracarpous and syncarpous fruits : i.e. reduction of the number of seeds, loss of dehiscence, transformation of the nutlet into a samara or modification of the pericarp wall, possi- bly of the fleshy fruit wall into a dry one. Most derived are infrutescences such as of Pandanus (Fig. 1), the pineapple or the fig.