426 REPRODUCTION. 



of which may, in suitable soil, give rise to a thrifty plant : the 

 new plants will in their turn produce new tubers likewise with 

 buds, and these again new plants, and so on in unlimited 

 succession. Nevertheless, the divisible organisms are for our 

 present purpose conveniently termed vegetable individuals. 1 



1103. Plants of the higher grade (Phaenogamous plants) are 

 propagated either by buds or by seeds. In the former case, a 

 portion of the axis with incipient leaves is separated from the 

 parent ; in the latter case, a new structure (the embryo) , capa- 

 ble of independent existence, is formed by means of a special 

 apparatus, the flower. In the flower, two sets of sexual or- 

 gans, the stamens, constituting the androecium, and the pistils, 

 constituting the gyucecium, produce by their conjoint action an 

 embryo, or undeveloped plant, within the seed. 



Reproduction by buds is non-sexual or asexual ; that by the 

 formation of an embryo is sexual. 



1104. Non-sexual reproduction (Agamogenesis) can be traced 

 through all classes of plants, from the higher, where it takes 

 place through proper buds, down to the very lowest, where it 

 takes place by a single cell dividing spontaneously to form two 

 or more separated individuals. 



1105. Sexual reproduction (Gamogenesis) likewise can be 

 traced through all classes of plants except the very lowest, 

 where it has not as yet been demonstrated to exist. As the 

 series is followed from above downwards, the flower gives place 

 to other structures, and the seed is replaced by simpler bodies, 

 known as spores. 



FERTILIZATION IN ANGIOSPERMS. 



1106. Flowering plants are naturally divided into Angio- 

 sperms and Gymnosperms : the former are distinguished by the 

 possession of a closed ovary in which the ovules are contained. 

 The latter have no closed ovary, and hence the ovules are naked. 

 A part of the reproductive apparatus is simpler in Gymnosperms 

 than in Angiosperms ; but owing to certain practical difficulties 

 in the treatment of microscopic material, the demonstration of 

 the reproductive process is less easy in the former than in the 

 latter. It is proposed, therefore, to begin with an examination 

 of the reproductive process, or fertilization, of Angiosperms. 



1 The view has been held by some that all the derivatives from one seed, 

 whether united or separated, constitute collectively a single individual. 



