30 Plant Tissue Culture 



of the cell as a physiological entity and to its fun- 

 damental totipotency. The whole gene mecha- 

 nism, as exemplified in somatic cells, seems to 

 lose its meaning without this concept. The regen- 

 eration of leaves and roots from tissues which are 

 neither leaf nor root points to the existence of 

 capacities which are called forth only by excep- 

 tional circumstances. Vochting's dissection ex- 

 periments suggest a similar explanation. Spe- 

 mann and his followers have obtained in their 

 transplantation experiments striking support of 

 this concept, for, while a piece of epithelium of a 

 melanotic amphibian is always melanotic (species 

 specific) in whatever host it may be grown (Fig. 

 3), it may form tail, or mouth, or eyelid, depending 

 on the position in the body in which it is placed 

 (Fig. 4) (Harrison, 1904, 413; Filatow, 1925, 402; 

 Spemann, 1936, 431; Schotte, 1932, 430). Some 

 transformations such as, for example, that from 

 fibroblast to macrophage are also known to take 

 place in animal tissue cultures (Ebeling and 

 Fischer, 1922, 391; Fischer, 1925, 406, 1926, 407). 

 There thus still seems to be much evidence to sup- 

 port Haberlandt's original concept and to lend 

 support to the hope that, while excised plant cells 

 have not yet been grown in vitro with the facility 

 which Haberlandt appears to have anticipated, 

 they will eventually be so grown. Such is the 



