Differentiation 



211 



scale, and the form of the leaf is a quantitative criterion of physiological 

 age. In cotton, maximum lobing of the leaf is reached at flowering, earlier 

 and later leaves being less lobed. The cyclical change proceeds more 

 rapidly in early-flowering than in late-flowering types, and conditions that 

 hasten flowering hasten lobing. Krenke believes that rate of change in 

 leaf shape is inherited and that early-maturing varieties may thus be dis- 

 tinguished in the seedling stage. 



PARTHENOCAKP1C 



FEMALE 

 FLOWERS 



^ 



GIANT FEMALE 

 AND INHIBITED 

 MALE FLOWERS 



Fig. 8-19. Cucurbita. Sequence of flower 

 types on a plant of the acom squash. 

 ( From Nitsch, Kurtz, Liverman, and 

 Went.) 



OJ 



NORMAL 



MALE 8 FEMALE 



FLOWERS 



NORMAL 

 MALE FLOWERS 



UNDERDEVELOPED 

 MALE FLOWERS 



Ashby has confirmed some of Krenke's conclusions but finds others very 

 doubtful. The possibility, however, of relating successive morphological 

 changes to physiological ones has important implications for the problem 

 of form determination. One may question Krenke's assertion that his 

 hypothesis is based on dialectical materialism, but the hypothesis itself 

 should be explored as one hopeful approach to morphogenetic problems. 



The bearing of Krenke's ideas on the problem of senescence is of in- 



