34 THE EVOLUTION THEORY 



of cells must be distributed over the whole surface of the plant, 

 each of which can in certain circumstances become the starting-point of 

 a bud. That is to say, each must contain, in a latent state, the complete 

 germ-plasm which is necessary for the production of an entire plant. 



We must therefore assume that, in the higher colony-forming 

 plants, germ-plasm is contained in a great many cells, perhaps 

 in all which are not histologically differentiated, and sometimes 

 even in those which are so, as, for instance, in the leaves of Be- 

 gonias. I suppose, therefore, that in the higher plants the process 

 of development implies a segregation of the determinant-complexes of 

 the germ-plasm, but that this takes place at a late stage, and that 

 in a much higher degree than among animals the individual or the 

 ' person ' carries with it germ-plasm in a latent state. To this must 

 be attributed the fact that the plant is not only able to make good its 

 losses in twigs and branches by sending out new shoots, but that 

 cuttings, that is, detached shoots, are also able to take root, and in 

 general to give rise to what is necessary to complete themselves 

 according to the position of the part in question. In the ontogeny 

 of animals, too, we must assume that it requires a liberating stimulus 

 to rouse the determinants to activity, that this stimulus is to • be 

 sought for in the influence exercised by the constitution of the cell 

 on the idioplasm contained within it, and that this constitution in 

 its turn is subject to influences from external conditions, including 

 the cell-soma itself. We may therefore suppose that, among plants also, 

 the germ-plasm latent in numerous cells only becomes active in whole or 

 in part according to the influences exerted on it by the state of the cell 

 at the moment ; but this varies with external circumstances, according 

 to whether the cell is exposed to light or lies under ground, according 

 as it is influenced by gravity, by moisture, chemical stimuli, and so on. 



It might be objected to this that it would be simpler not to 

 assume a segregation of the germ-plasm into determinant-complexes 

 at all in order to explain the process of development, but rather to 

 credit each cell with a complete equipment of germ-plasm from the 

 beginning to the end of the ontogeny, and to attribute the differences 

 in the cells, which condition the structure of the plant and its 

 differentiation, solely to the different influences, external and internal, 

 to which the cell is exposed, and which rouse some determinants to 

 activity at one part and others at another. Perhaps the botanists 

 would be more readily reconciled to this idea, but it seems to me that 

 there are two points which tell against the possibility of its being 

 correct. In the first place, it is far from being established that every 

 cell in the higher plants is capable of giving rise, under favourable 



