202 BOTANY PART i 



which in Angiosperms makes its way by means of the style to the 

 cavity of the ovary and through the outer layers of sterile cells of 

 an ovule to the egg-cell. When an open connection has been estab- 

 lished between the pollen tube and the egg-cell, the latter is fertilised 

 by a nucleus from the pollen tube. The fertilised egg develops 

 within the enlarging ovule to a multicellular embryo, which becomes 

 segmented into the COTYLEDONS, RADICLE, and PLUMULE. The ovule 

 becomes the SEED, the outermost tissues giving rise to the seed-coat. 



THE SEED, WHICH IS SHED WHEN RIPE AND SERVES TO MULTIPLY THE 

 PLANT, IS THUS A FURTHER DEVELOPED OVULE ENCLOSING AN EMBRYO. 



The ovary also develops further after fertilisation and gives rise to 

 the FRUIT. When this remains attached to the plant it opens when 

 mature by splits, pores, or the separation of a lid," in order to liberate 

 the seeds (capsule). Often the whole fruit enclosing the seed is 

 separated from the plant, as in the case of berries, nuts, and stone- 

 fruits. 



The seeds or the detached fruits are adapted for dispersal ( 10 ) 

 like other reproductive bodies. This is effected by the same means 

 as the transport of pollen, by currents of air or water, by means of 

 animals, and sometimes by special constructions or movements of the 

 plant. The construction of seeds and fruits shows adaptation to the 

 mode of dispersal (cf. the Special Part). 



On the seeds being thus sown, GERMINATION ( 101 ) commences after 

 a longer or shorter time. As a rule the root of the embryo emerges 

 first, rupturing the seed-coat. Since this is often very hard, special 

 regions for the exit of the root may be present in it (e.g. in the Coco- 

 nut). In the further development of the shoot of the seedling, mani- 

 fold differences become apparent in different kinds of plants ; these 

 will be described in the Special Part. The seedling at first grows 

 at the expense of food materials provided by the parent plant and 

 stored in the seed. 



A peculiar type of asexual reproduction (apogamy) occurs in some flowering 

 plants and replaces the sexual reproduction. Within the ovule and replacing the 

 suppressed egg cell, asexual embryos are developed from other cells ( 95 ). The seeds 

 thus include no product of sexuality but have become organs of vegetative repro- 

 duction. This formation of adventitious embryos is commonly associated witli 

 POLYEMBRYONY, i.e. the formation of a number of embryo plants in a single seed 

 (Funkia ovata, Citrus aurantium, Caelebogyne ilicifolia, etc.). 



2. The Process of Cell-Fusion in Fertilisation and its Results. 



The actual process of fertilisation in its simplest form can be best 

 observed in those lower organisms with similar gametes (Fig. 229). 

 In these it can be easily shown that not only the cytoplasm of the 

 two cells but sooner or later the nuclei also fuse. When the male 

 cell possesses chromatophores, which in many Algae (Florideae, Chara, 

 etc.) is not the case, they do not fuse with those of the female cell. 

 They either coexist in the fertilised cell or, when a constant number 



