2l8 THE GERM-PLASM 



nary nutrition is required in order to incite them to form buds. 

 The series of cells which lead directly to the cells of these buds 

 must be looked upon as the main germ-tracks, using the term 

 in de Vries's sense. According to Seeliger's researches, how- 

 ever, budding takes place from other regions as well as the 

 ordinary ones in certain Polyzoa, e.g., Pedicellina. If the crown 

 is lost in this animal, so that only a stump of the stalk remains, 

 new crowns are produced on the end of the stalk ; and in this 

 case, therefore, budding orighiates in the flat epitJielial cells 

 characteristic of the ectoderm, which did not previously appear 

 to be capable of proliferating at all. This is another instance of 

 the presence of accessory germ-tracks. The cells of the epi- 

 dermis are provided with blastogenic germ-plasm, although they 

 do not as a rule take part in the formation of buds, but only 

 give rise to them in response to unusual stimuli. These cells are 

 just as much exposed to destruction as are those of the Hydroid 

 polypes, and we need therefore not be surprised that arrangements 

 for budding should have been made in the stalk, even w'ere we 

 not aware of the fact that in Pedicellina, under normal condi- 

 tions, the crowns drop off periodically from the stalk, and are 

 replaced by others which bud out afresh. This process cer- 

 tainly occurs at the upper end of the stalk, but it is quite com- 

 prehensible that it would be advantageous for the lower end of 

 the stalk also to be provided with blastogenic idioplasm. 



The arrangement which exists universally in the higher plants 

 for the production of adventitious buds is, in my opinion, to be 

 explained in a similar manner. In this group of organisms the 

 cambium layer in particular is provided with the means of re- 

 placing lost leaves and entire shoots. This obviously affords an 

 important protection against numerous enemies — such as insects 

 more especially — the number of which is often incalculable. It 

 is therefore not surprising that such an arrangement — viz., the 

 addition of unalterable germ-plasm to the cambium cells — is 

 here met with. 



5. Galls 



De Vries has also brought forward the question of the formation 

 of galls as furnishing an additional argument against my views. 

 In his opinion the production of galls proves that a vegetable 

 cell, even when it exhibits a specific histological differentiation, 

 contains the primary constituents of every other kind of cell in 



