THE FORMATION OF GERM-CELT5 215 



many intermediate stages between these two, for at the present 

 day the two kinds of cells in I'o/vo.v h3.rd\y dilTeras much as do 

 the somatic- and germ-cells in the case of the higher organisms. 

 The somatic cells have nevertheless entirely lost the capacity of 

 reproducing the entire organism. 



Transitions between these two kinds of cells could naturally 

 only arise by the germ-cells first becoming only slightly differ- 

 entiated from the somatic cells, and could not have been pro- 

 duced, as de Vries thinks, owing to all the cells containing 

 germ-substance in a more or less latent condition from the first. 

 There is no germ-substance in the somatic cells of Volvox, 

 which, figuratively speaking, have only just become differentiated 

 from the germ-cells. If the latter are artificially removed from 

 a colony, the somatic cells continue to exist for a long time, but 

 they do not give rise either to new germ-cells or to a new colony. 



And why should they do so ? Of what advantage would this 

 be to the species, since millions of individuals, each of which 

 again produces daughter-individuals, exist in the same pond? 

 The ordinary process of multiplication is so vigorous that special 

 means for ensuring the existence of the species are unnecessary. 



Such means hai'e, however^ been adopted in very many, if not 

 by far the greater nu?nbe} , of the tnore highly organised plants. 



The power possessed by fungi and mosses of reproducing a 

 new individual from any bit of the plant under favourable condi- 

 tions, has been supposed to contradict my view. But I do not 

 see what prevents us from regarding this power as an adaptation 

 for ensuring the existence of a species surrounded by dangers 

 of all kinds. When the top of a toadstool is knocked off, a new 

 one is formed (Brefeld) ; and this arrangement is obviously of 

 great use in the preservation of the species. An entire liverwort 

 can be regrown from the smallest fragments of the plant (Voch- 

 ting) . Why therefore should the assumption be improbable that 

 this power has been acquired in order to insure the persistence 

 of a species the existence of which is threatened by every sudden 

 drought ? My knowledge of plant life is not sufficient for me to 

 be able to support this statement in detail, but other facts will, I 

 think, to some extent confirm my opinion from the opposite point 

 of view. 



Why is this power of regeneration not possessed by adult 

 ferns and horse-tails? If a frond of a fern is cut off, it is not 

 reproduced from the stalk, and even the individual pinnae cannot 



