458 



PART III. THE CLASSIFICATION OF PLANTS. 



FIG. 295. Sections of ripe seed. A Nux vomica, 

 showing E endosperm. B Piper, showing both endo- 

 sperm E, and perisperm P. C Almond, devoid of 

 endosperm; the testa; e embryo; to its radicle; 

 c c its cotyledons. 



cell (female pronucleus) approach each other and fuse into one, 

 the two protoplasms likewise fusing. Fertilisation is now com- 

 plete ; in consequence, 

 the oosphere surrounds 

 itself with a cell- wall, 

 becoming the oospore, 

 and begins to develope 

 into the embryo-sporo- 

 phyte. Further details 

 are given in the sec- 

 tions on Gymnosperms 

 and Angiosperms respec- 

 tively. 



The Results of Fertilisation. The most direct result of fertilisa- 

 tion is the development of the embryo from the fertilised oosphere, 

 a process which involves the conversion of the ovule into the seed. 

 But the effect of fertilisation is not limited to this : other parts 

 of the flower are affected in such a way that they undergo marked 

 changes in structure, accompanied by considerable increase in size, 

 the product being the structure known as the fruit (p. 88). In 

 some cases the carpels only are affected, becoming either fleshy 

 and succulent (e.g. Plum), or dry and hard (e.g. Poppy) ; in others, 

 the floral axis becomes fleshy (e.g. Strawberry); in others again 

 the perianth. leaves also (e.g. Mulberry). It is convenient to 

 regard as true fruits only those which are developed from the 

 gynaeceum alone ; and as false fruits, or pseudocarps, those in the 

 formation of which other parts of the flower or of the inflorescence 

 take part. 



The seed (p. 88) is produced from the ovule, as a consequence of 

 the fertilisation of the female cell contained within the ovule: its 

 characteristic feature is that it contains an embryo. The seed 

 (Fig. 295) may contain little or nothing but the embryo, in which 

 case it is said to be exalbuminous (e.g. Pea, Bean, Sunflower, 

 Almond, Oak) : or it may contain, in addition to a small embryo, 

 a considerable portion of the female prothallium (endosperm), when 

 it is termed albuminous (e.g. Grasses and most Monocotyledons, 

 Ranunculaceae) : in a few rare cases the albuminous seed contains, 

 in addition to the embryo and endosperm, some of the nucellar 

 tissue of the macrosporangium which is termed per/sperm (e.g. 

 Piperaceae, Nympheeacese, Zingiberaceae) : but generally, as in the 

 Musaceae, Cannaceae, Caryophyllaceae, Chenopodiaceae, Amararit- 



