222 Plant Tissue Culture 



genesis, the causal factors involved in the differen- 

 tiation of bast-fibers, stone-cells, medullary ray 

 cells, phloem tube elements, and of true meristems, 

 all from the same parenchymatous elements, are 

 also problems open to attack by tissue culture 

 methods. 



These suggestions merely serve to point out 

 some of the as yet essentially untouched fields 

 opened up by the development of this technique. 

 The history of the progress of science is a history 

 of such tools. 



SUMMAKY 



In the study of the origin of form and function, 

 that is, of morphogenesis, tissue culture methods 

 provide a means of isolating cells, organs, and tis- 

 sues from the morphogenetic influences of neigh- 

 boring cells, organs, and tissues and placing them 

 in controlled environments. Questions of the 

 effects of growth substances or ''hormones," of 

 chemical and physical gradients, and of cytoge- 

 netic factors can be approached by this means with 

 considerable hope of success. 



