202 Plant Tissue Culture 



virus, Jensen's No. 16 strain of tobacco mosaic 

 virus, and some other virulent types (White, un- 

 published). Interestingly enough, no method has 

 yet been found for inoculating such cultures (they 

 must be isolated from systemically infected 

 plants), so that there is no danger of a virus-bear- 

 ing culture, once established, ever becoming con- 

 taminated with another virus (White, 1934, 438). 



Tissue cultures have to date not been tested as 

 hosts for phanerogamic parasites such as Cuscuta, 

 Viscum, etc., but should prove useful in the study 

 of phanerogamic host-parasite relations. 



One field of investigation in which tissue cul- 

 tures promise to be extremely useful, which repre- 

 sents essentially an extension of the nutrition 

 studies mentioned above, is that covering the 

 effects of toxic or injurious substances, either of 

 organic or inorganic origin, on the behavior of the 

 tissues of such cultures. The reaction to indole 

 acetic acid mentioned above is an excellent exam- 

 ple and serves to show the sorts of observations 

 which are possible in this field using even very 

 simple methods (Figs. 48, 51, 52). The reaction of 

 excised carrot tissue to colchicine has also been 

 studied, by Duhamet (1939, 210). 



Histology and Cytology 



Tissue and organ cultures furnish unusually 

 clean, uniform, easily handled material for histo- 



