Chemical Factors in General 373 



line stimulates the differentiation of protoxylem in roots of cotton and 



beans. 



By adding certain chemical substances to the medium, Tatum, Barratt, 

 and Cutter ( 1949 ) produced various nonheritable morphological changes 

 in Neurospora and Syncephalastrum which they termed paramorphs. 

 Anionic surface-active agents such as Aerosol induced the formation of 

 compact colonial paramorphs. Sorbose proved to be the most effective 

 paramorphogen. Discovery of the mechanisms by which these substances 

 cause the production of such specific forms in these very simple organisms 

 might yield important information on the origin of forms at higher levels. 



There is a considerable group of chemical substances, the vitamins, 

 which are of great importance in animal nutrition. Many of them are 

 synthesized by plants, and some are now known to be essential for the 

 growth of certain plants or plant structures. Vitamin B x (thiamin), for 

 example, can be shown to be necessary for the growth of excised roots in 

 culture, but it is synthesized in the shoots. Nicotinic acid also seems to be 

 essential for root growth, but what other vitamins may also be necessary 

 for the life of plants is not certainly known. All the vitamins are effective 

 in extremely small concentrations. 



The morphogenetic importance of the vitamins for plants seems not 

 to be very great. Reid (1941) has evidence that vitamin C affects cell 

 size in the meristematic region, and there are a few similar instances. 

 Schopfer (1950) has reviewed the problem of the vitamins in morpho- 

 genesis. 



