CHAPTER IV. — SPECIAL PHYSIOLOGY OF REPRODUCTION. 767 



inspection between merely histogenic and truly reproductive 

 cytoplasm. 



§ 19. Vegetative Multiplication. This mode of reproduc- 

 tion is distinguished as vegetative, because it is carried on by the 

 vegetative organs of the plant, and, in the simpler cases, it is not 

 distinguishable from the ordinary processes of growth; though, 

 in its higher forms it approximates to reproduction by spores. 

 The simpler cases refered to are those of unicellular organisms : 

 these, when they have reached by growth their characteristic 

 limit of size, undergo cell-division, with the result that each new 

 cell constitutes a new individual : here, multiplication is effected 

 by a purely vegetative process, which, in a multicellular plant, 

 would merely result in an increase in the number of the cells of 

 which the individual consists. Much the same thing occurs in 

 higher plants when (as in many Bryophyta, and in rhizomatous 

 Pteridophyta and' Phanerogamia) the main shoots die away, and 

 the isolated lateral branches constitute new independent in- 

 dividuals. Something of a similar kind also takes place in the arti- 

 ficial multiplication of plants by means of cuttings : in many plants, 

 but by no means all, if a shoot be cut off and be kept under 

 favourable circumstances Avith its cut end in suitable soil, the 

 cutting will complete its segmentation by the development of 

 roots, and will then be a new individual. Not uncommonly, 

 certain parts of the body may become more or less specially 

 modified to effect vegetative propagation: for instance buds 

 become developed into bulbs or into bulbils (see p. 68), or portions 

 of the stem or the root become tuberous. But the specialisation 

 which may be regarded as the high est of all, because it approaches 

 most nearly to spore-reproduction, and involves the entire develop- 

 ment of all the the new members, is that_of_gernmae in which the 

 vegetative reproductive body is not merely a modified member of 

 the parent, but is a special dev^elopment consisting in some cases 

 of only a single cell {e.g. gemmas of some Algae and Liverworts, 

 p. Q7 ; oidium-cells of Fungi, p. 274). Something of the same 

 kind occurs amongst the higher plants, such as some Ferns, 

 Bryophyllum, etc., where an entirely new structure, a bad, is 

 developed on the leaf, and produces stem, leaves and roots; it is 

 in this way that Begonias are artificially propagated. 



An interesting artificial mode of vegetative propagation is that known as graft- 

 ing or budding, in which a young shoot or a bud, termed the scion, of one plant 

 is inserted into the stem of another, though allied plant, the stock. Generally 



v. s. B. 3d 



