460 PART III. THE CLASSIFICATION OF PLANTS. 



as caruncles or strophioles), occur in certain plants : thus in the 

 Violet and the Celandine (Chelidonium) an elevated ridge marks 

 the course of the raphe, and in the Willow-herb (Epilobium) a 

 tuft of hairs springs from the chalaza. 



The most important point to be considered is, however, that of 

 the structural conditions which determine the production of a seed 

 in the Phanerogams, the feature which sharply defines this group 

 of plants from all others. The structural conditions are briefly as 

 follows : the macrospore (embryo-sac) is not set free from the 

 macrosporangium (ovule), as is the case in the heterosporous 

 Pteridophyta.; nor does the macrosporangium itself separate from 

 the plant producing it until it has ripened into the seed: this 

 being so, the macrospore germinates inside the macrosporangium, 

 producing there the female prothallium with its reproductive 

 organs: fertilisation of the oosphere, as also the development of 

 the embryo from the oospore, takes place inside the macrospore ; 

 and thus the seed is formed. If the macrospore were set free 

 from the macrosporangium, no seed would be formed; but in that 

 case the condition of things would be that which actually exists 

 in the higher heterosporous Pteridophyta, such as Selaginella. 



Some seeds can germinate as soon as they are shed : but, for 

 thi* most part, they onlv do so after a period of quiescence, though 

 thev may lose their germinating power if this period be too pro- 

 longed. 



The Dissemination of the Seed. Fruits are either dehiscent, so 

 that the seeds escape, or are indehiscent : in the former case the 

 seeds, and in the latter case the fruits, present various adaptations 

 for ensuring their dispersion. The most conspicuous are those 

 which ensure dispersion by the wind : of this nature are the wing- 

 like appendages of the fruit in the Maple, Ash, Ailanthus, Elm, 

 etc. ; and of the seed of Pinus, Tecoma, Catalpa, etc. : also the 

 hairy appendages of fruits (e.g. the pappus of Composite, the 

 feathery style of Clematis, etc.), and of seeds (e.g. on those of 

 Grossypium the Cotton-plant, Willow, Poplar, Asclepias, etc.). 

 Other adaptations ensure dispersion by animals; such are the 

 hooks on fruits (forming burrs), as in various Boraginaceae, 

 Composite, Gralium, etc. : the succulence and agreeable taste of 

 many indehiscent fruits also promotes the dispersion of the seeds, 

 the fruits being eaten by animals and the seed being protected 

 from digestion by hard protective tissue either in the fruit (endo- 

 carp) or in the seed-coat (testa). In some cases (e.g. Ecljallium 



