104 The Individtial Tracks 



then, that an apparently uninterrupted Hne of transitional 

 forms leads from the germ-tracks to the somatic tracks. 



In the cell-pedigrees of one-celled organisms and of 

 homoplastids all the twigs are primary germ-tracks. In 

 the next higher plants primary and secondary germ- 

 tracks are to be distinguished and, the more highly the 

 organism is differentiated, the more are the latter pushed 

 into the background. They are lacking in the higher ani- 

 mals. But in such highly developed Thallophytes as the 

 fungi, and even in the mosses and liverworts, it is ap- 

 parent that all twigs in our picture have still the value of 

 germ-tracks. At least sterile side-twigs, that is, somatic 

 tracks, have not yet been demonstrated there. But, in the 

 case of the vascular plants, most of the tissue-cells, at 

 least when fully developed, can without doubt no longer 

 reproduce the species. Therefore the somatic tracks form 

 here an important part of the picture. 



But let us now compare the somatic tracks of the vas- 

 cular plants with the secondary germ-tracks of the Mus- 

 cinese. Were not the significance of the latter known to 

 us through the investigations of Pringsheim and Voch- 

 ting, we would designate at least some of them as so- 

 matic tracks, for the question can be decided only by the 

 presence or absence of the power of reproduction. On 

 the other hand, it may possibly be shown, at some future 

 time, that some somatic cells of the vascular plants have 

 this power after all, and what we now call somatic tracks, 

 we will then have to regard as secondary germ-tracks. 



The somatic tracks have obviously developed phyloge- 

 netically from the secondary germ-tracks. Not suddenly, 

 however, and at a leap, but quite gradually. The loss of 

 the power of reproduction makes them such. By this 

 means, however, only an adaptation, and no intrinsic dif- 



