Morphogenesis 221 



the nature of this incompatibility. Gautheret 

 (1935, 15) has carried out experiments of this type, 

 though for quite a different purpose, in his pre- 

 liminary study of heterologous and homologous in 

 vitro grafts, which indicate the feasibility of this 

 sort of approach (Fig. 64). (See also Figs. 69, 

 70.) 



The tissue culture technique has recently per- 

 mitted the transfer of one problem group already 

 mentioned, the "crown gall problem," from the 

 field of pathology to that of experimental morpho- 

 genesis with extremely important implications. 

 Tissues isolated from secondary or metastatic 

 crown gall tumors have been grown in tissue cul- 

 ture (Fig. 19). Here they maintained a rapid, 

 disorganized type of growth (Fig. 67) which ex- 

 pressed itself, upon reimplantation into healthy 

 hosts, in the production of new tumors. The tis- 

 sues were shown to be free of bacteria. The 

 tissue culture technique has thus permitted the 

 experimental manipulation of crown gall tissues 

 free of the original pathogen and the study of the 

 factors involved in the origin of the tumefacient 

 property of the cells themselves. It thus offers a 

 new approach to problems of the origin of malig- 

 nancy (White and Braun, 1941, 335, 1942, 336, 337; 

 Braun and White, 1942, 436). 



The physiological aspects of cellular morpho- 



