Primary and Secondary Germ-Tracks 95 



quently overtop the main-stem which thus, not infre- 

 quently, is in the back-ground of the picture. Or, more 

 correctly speaking, there is no real main-stem, or at least 

 hardly any. 



6. The Secondary Germ-Tracks 



In the higher animals the secondary germ-tracks are 

 lacking, in the vegetable world they are widely distrib- 

 uted. It is especially this circumstance which makes the 

 study of cell-pedigrees in the vegetable kingdom so much 

 more profitable than in the animal world, and the objec- 

 tions raised by Sachs, Strasburger, and other botanists 

 against Weismann's conception regard essentially the cir- 

 cumstance that the latter did not give due attention to 

 the secondary germ-tracks. 



The secondary germ-tracks can by no means be re- 

 garded as exceptions. In no tree, in no shrub are they 

 lacking. Among perennial plants they are, if not of gen- 

 eral occurrence, at least very widely distributed, and only 

 the annual and biennial species are without this kind of 

 propagation. On the other hand the adventitious forma- 

 tions exhibit so many forms, such high differentiations, 

 and such beautiful adaptations, that they also are not 

 placed in the background, in this respect, as compared 

 with the primary germ-tracks. 



For our purpose three cases are to be kept separate : 



1. Nearly all cells of the body can develop into new 

 individuals. 



2. Adventitious buds arise only from definite cell- 

 groups or cell-tracks preformed to this end, namely : 



a. from meristematic tissues, 



b. from mature cells. 



The phenomena of regeneration of the Thallophyta 



