228 PART III. PHYSIOLOGY. [ 55 



distinguished from adult, protoplasm. But it must not be over- 

 looked that all embryonic protoplasm is not necessarily reproduc- 

 tive : and it is interesting to trace the differences in this respect, 

 presented by various kinds of embryonic protoplasm. To begin 

 with, there is no doubt that the merismatic cells of the cambium 

 are embryonic : but they are not at all reproductive, for they 

 cannot give rise to a new member, still less to a new organism ; 

 they can only add to the bulk of the body of which they form 

 part, by the development of new tissue. Again, the protoplasm 

 of a growing-point is embryonic, but it is only imperfectly repro- 

 ductive ; it possesses this property to the extent that it not only 

 contributes to the increase of the member to which it belongs, 

 but also developes new members. Finally, the protoplasm of a 

 reproductive cell, such as a spore, is embryonic and is completely 

 reproductive ; for it does not in any degree contribute to the bulk 

 of the parent-organism, but gives rise to a new individual. 



55. 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 referred 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 

 artificial 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 with 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 be- 

 come developed into bulbs or into bulbils (see p. 25), or portions 

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



