Genie Control of Development 407 



which in some completely unknown way finally control the function of 

 the hormonic glands. 



An interesting fact which shows that the substrates for hormonic 

 action belong somehow to the same genie reaction system is found in 

 the phenomenon of prothetely. This means that parts of the body may 

 be in advance of the development of the rest. One example is the 

 Lymantria dispar caterpillar, in which only the antennae undergo the 

 pupal molt while the caterpillar itself may live long beyond the normal 

 span of its life without molting any more. In this case ( Goldschmidt, 

 1923<i) it was found that the condition was hereditary in a definite 

 line. How this mutant (not analyzed further) localizes the hormonic 

 action and prevents it in the rest of the body is difficult to visualize. 



Thus far we have discussed the relations between genie actions 

 and hormones only in animals. Actually one should expect that much 

 more insight could be gained from plants (see Thimann, 1952; Ward- 

 law, 1952). It seems that in plants, hormones (phytohormones, auxins, 

 etc.) play a role in morphogenesis which is incomparably more im- 

 portant than the corresponding role of hormones in animals. (I am 

 speaking now only of genuine, diffusible hormones. ) There can be no 

 doubt that morphogenesis is impossible in plants without such hor- 

 monic action and that, therefore, phytohormones should constitute a 

 major subject of physiological genetics in plants. In spite of an im- 

 mense literature on the subject, it seems that the genetical side of the 

 problem has hardly been touched; this means the comparison of 

 hormonic action under known genetic differences. If a mutant of a 

 snapdragon changes the zygomorph flower into a radiate one, we 

 should like to know whether a different distribution of a phytohormone 

 can be located in the flower primordium. Many types of experiments 

 can be imagined which would link genie differences with phyto- 

 hormones as morphogenetic substances. Very few are available. For 

 example, in Hyoscyamus niger there are annual and biennial forms, 

 differing in a single pair of mutant loci. Melchers (1937; see 1952) 

 grafted shoots of annual flowering plants on first-year biennial stocks, 

 with the result that the latter flowered. The reciprocal graft gave 

 corresponding results. This might mean that the mutant locus was 

 concerned with production or inhibition of a flowering hormone. How- 

 ever, since both races will eventually produce flowers, it might also 

 mean that the always present hormone reaches a threshold level 

 sooner or later. In neither case can we say that the genie action 

 produces a morphogenetic substance, a hormone, which forces devel- 



