408 Action of the Genetic Material 



opment into the path of specific processes leading to a flower. It is 

 more probable that the hormone concentration does not determine a 

 flower but is one of the chemical conditions for allowing the genically 

 determined flower formation to take place sooner or later. This situ- 

 ation may be compared to that of the molting hormones of insect 

 larvae; in both cases the presence of a hormone is needed for the 

 initiation of a genically controlled over-all process of development. 

 Annual and biennial growth would then be comparable to four and 

 five molts in the insect. 



A similar experiment was made by Stein ( 1939 ) . A sterile mutant 

 of snapdragon, forming a non-flowering axis, was grafted to normal 

 stock and developed flower buds. The comparison with the insect 

 case is enhanced by the fact that these "florigens" are not specific, just 

 as with the molting hormones, in both cases demonstrated by grafting. 

 We suggest, further, that Melchers' experiments on vernalization (see 

 II 2 B ) point in the same direction and that, mutatis mutandis, Ham- 

 merling's work on Acetabularia (III 2) can be interpreted in the same 

 way. Another point of comparison between the animal and the plant 

 is the role of timing. Many botanists more or less accept Lysenko's 

 phase theory, which, in zoological terms, and stripped of Lysenko's 

 mystical connotations, means that environmental or genie action can 

 take place only when the plant has reached the proper level of com- 

 petence. However, many facts do not agree with this theory, which 

 interests us here only so far as it means that the time dimension, in the 

 form of successively developing competence, would play a role also 

 in the determinative processes of plants. 



The facts just mentioned and the extensive body of facts on phyto- 

 hormones suggest that what we called the short cut via hormonic 

 action for integrating more complicated developmental processes plays 

 a superior role in the system of genetic determination of plants, a 

 view which is held especially by Went (see Went and Thimann, 

 1937). We expect, therefore, the most important results for our 

 problem when plant geneticists, following Melchers, will use the 

 physiology of hormonic action to build up the special type of physio- 

 logical genetics which is accessible only in plants. Unfortunately, thus 

 far the attack has been only physiological and has not yielded much 

 information for the geneticist. Wardlaw (1952) has recently scruti- 

 nized the available material in order to find links between hormone 

 physiology, morphogenesis, and genetics. His conclusions are not very 

 encouraging. To quote: "The data . . . make it clear that the in- 

 ception and subsequent development of the several organs and the 



