ZIMMERMAN: FORMATIVE INFLUENCES 113 



different strains of virus so do they vary with the different active growth sub- 

 stances. A characteristic virus-like type of response is illustrated in figure 4 for 

 three different compounds applied to two different species of plants. The 

 chemically induced responses have the characteristic modifications of leaves 

 showing clearing of the veins, irregular shape, light and dark portions of tissue, 

 etc. The present results appear to lend support to the claim that virus diseases 

 result from natural chemical influences. 



The mechanism in the plant through which these chemicals act is not well 

 understood. It is fairly certain that living protoplasm has many potentialities 

 for expressing itself and that environment determines which of these can de- 

 velop. The so-called "normal" characters of a plant are but a partial expression 

 of the range of possibilities of which the protoplasm is capable. Natural varia- 

 tions in the pattern of leaves of certain species of plants growing in different 

 environments lend support to this theory. The influences which regulate growth 

 must deal with undifferentiated meristems made up of uniform cells and in some 

 way cause them to give rise to specialized cells which in turn give rise to new 

 tissues and new organs of plants. Sinnott (2) is of the opinion that the cyto- 

 plasm plays an important role in "the construction of a pattern." It seems 

 reasonable to assume that modified organs result from the influence of the 

 chemicals acting upon the cytoplasm rather than upon the more stable nucleus. 

 Each chemical constitutes a different environment and, therefore, permits dif- 

 ferent potentialities of the protoplasm to develop. This, at best, is only an as- 

 sumption but may in time help us to interpret the qualitative differences in 

 responses resulting from treatment with different growth substances. 



The molecular configuration as a whole rather than any part of the mole- 

 cule appears to determine physiological activity. A slight shift in the position 

 of a substituted group, a change from chlorine to an amino group, or a shift in 

 the linkage of the chain to the nucleus may activate or inactivate a molecule. 



In addition to the exact nature of the molecule, the constitution of the re- 

 ceptor tissue in the plant is important. First, the genetic constitution of the tis- 

 sue plays an important part, and second, the location in the organ and the age 

 of the tissue are determining factors. 



Explanation of figure 3 



Formative influence of 2-chloro-3,5-diiodobenzoic acid. A. Left, control ; middle, term- 

 inal portion of tomato plant after stem had been treated with a lanolin preparation (20' 

 mg./g.). Note miniature flower. Right, two abnormally large individual flowers (instead 

 of clusters) formed after one axillary shoot began to recover from the effects of the 

 chemical influence. B. Left, control ; right, terminal portion of the plant which had been 

 given soil treatment of 2-chloro-3,5-diiodobenzoic acid (4 mg. per pot applied in 50 cc. of 

 water). Note abnormally small flowers on 2 clusters and recovery of axillary shoot with 

 abnormal flower cluster. 



