Difference Between Somatic and Germ-Tracks 105 



ference is conferred. It is true that, through further 

 adaptions, the differences may have become greater and 

 greater; the use of the power of reproduction, at first 

 limited to less and less frequent cases, may finally have 

 become quite impossible by the loss, not only of the adapt- 

 ive, but also of the inner conditions thereto. Doubtless 

 all transitions to the non-nucleated spore-sacs will have 

 been made. 



But, in the plant world, by far the greatest number 

 of the somatic tracks are evidently still so much like the 

 secondary germ-tracks that we cannot assume an essential 

 difference between them. This is most clearly demon- 

 strated in those cases where homologous organs among 

 allied species consist, in one of them, of somatic tracks 

 only, while the other possesses secondary germ-tracks in 

 addition. 



The most instructive illustration is given in the pseudo- 

 somatic germ-tracks of the begonias. 20 Phylogenetically 

 these have obviously originated from tracks that we should 

 call somatic. But the very circumstance that, in the pro- 

 cess of the formation of species, this power of reproduc- 

 tion can make its appearance in cells in which it is lacking 

 in almost all the other phanerogams, teaches us that this 

 absence is only adaptive, I might almost say only apparent. 

 We are therefore compelled to attribute to the epidermal 

 cells of the leaves of the phanerogams in general a latent 

 power of reproduction. Yet they remain recorded as 

 somatic tracks in our empirical picture. Nevertheless it 

 seems perfectly clear to me that the difference is not quali- 

 tative. 



Furthermore, the correctness of this conception is cor- 

 roborated by the not at all infrequent instances where 



2 Cf. p. 100. 



