GROWTH AND DEVELOPMENT OF THE INFLORESCENCE AND FLOWER 



509 



be few biologists now who doubt that genie action pervades all mor- 

 phogenetic development, and that many of the minutiae of floral varia- 

 tion in hybrids and varieties are due to specifiable genes, to small 

 groups of genes, or to polygenes, there is a danger that the eflFects of 

 extrinsic factors in morphogenesis may not always be sufficiently ap- 

 preciated. 



In studies of the physiology of sexuality', J. Heslop-Harrison ( 1959) 

 has shown for different species that major changes can be induced in 

 the structure and function of the floral organs by varying external fac- 

 tors such as temperature and light, and by the application of exogenous 

 auxin. Y. Heslop-Harrison and Woods ( 1959 ) have shown that when 

 genetically male plants of dioecious Cannabis sativa L. are grown 

 under short days and low night temperature, a high proportion of the 

 flowers formed are intersexual, and a considerable amount of meristic 

 variation, fusions, and adnations is found among the male flowers 

 (Figure 13). The intersexuality in male flowers consists in a "trans- 

 formation of stamens to carpellate or intermediate structures." In some 

 species one or other of the sets of reproductive organs can be more or 

 less completely suppressed in what are normally hermaphrodite flowers 

 (J. Heslop-Harrison, 1960). J. Heslop-Harrison has also shown that 



Figure 13. (a) , Cannabis sa- 

 tiva L. Normal stamen and 

 stamens from flowers of male 

 plants which were exposed to 

 low night temperatures dur- 

 ing photoperiodic induction, 

 showing (b to /) various 

 forms of branching and fu- 

 sion. Magnification: about 

 twelve times. (After Y. Hes- 

 lop-Harrison and Woods, 

 1959.) 



