REPRODUCTION. 663 



crystal will, under appropriate conditions, grow into a large 

 one, so the protoplasm of the spore, possessing the power of 

 growth and of cell-division, will, under favourable conditions, 

 grow into an individual resembling that from which it was 

 derived. 



Without expressing any opinion as to the propriety of 

 Naegeli's assumption of the idioplasm, we simply regard the 

 reproductive capacity as being one of the fundamental pro- 

 perties of protoplasm (see p. 6). From this point of view 

 we cannot but regard the assumption of reproductive gemmules 

 in the theory of Pangenesis, and of a special "reproductive 

 substance " as in Weismann's theory, as altogether un- 

 necessary. Just as it is superfluous to suppose that the repair 

 of a broken crystal, to return to our illustration, is due to the 

 presence of gemmules or of a special reproductive substance, 

 so also is the supposition superfluous to explain the de- 

 velopment of roots by a cutting. 



But, as we have seen, it is not all the cells of a complex 

 individual that are capable of reproduction. Only those are 

 capable which are in a particular condition, a condition which 

 we may term, with Strasburger, the embryonic condition. 

 This condition of the cell doubtless depends mainly on the 

 nucleus, and the appropriate state of the nucleus may be 

 determined, as Strasburger suggests, by the presence of an 

 adequate proportion of nucleo-idioplasm. 



From this point of view, the facts of vegetative repro- 

 duction are susceptible of ready explanation. Vegetative 

 reproduction is effected by means of what we may term em- 

 bryonic somatic cells. In a growing plant such cells are 

 always present, and give rise to new organs and tissues. 

 When a portion of a plant containing such cells is isolated 

 and placed under favourable conditions, these cells give rise 

 to the members necessary to complete the segmentation of 

 the imperfect individual. 



It may, however, happen that a part of a plant which con- 

 tains no embryonic cells, may subserve vegetative repro- 

 duction ; for instance, the propagation of Begonias from 

 pieces of leaf: probably all cases of leaf-proliferation are 



