132 • A Miscellany 



ization holds that pistillate flowers represent a fuller intensity of 

 flowering than staminate flowers; thus, with photoperiodic plants, 

 prolonged short-day treatment favors pistillate expression relative 

 to staminate in SDP, whereas long-day treatment does so in LDP. 

 For example, in the LDP spinach, normally dioecious, short days 

 following long-day induction cause the formation of some staminate 

 flowers on plants that would normally produce only the pistillate, 

 thus making the treated plants monoecious (see Heslop-Harrison, 



1957). 



The factors that affect sex expression in plants with diclinous 

 flowers may affect even plants with hermaphrodite flowers in a 

 similar fashion. One particularly interesting example, dealing with 

 the effect of photoperiod, has recently been studied by J. and Y. 

 Heslop-Harrison (1958a,b). The plant is Silene pendnla, an LDP 

 in that flowering does not occur with 8 hours of daylight but is 

 brought about by supplementing this to 21 hours with light of 

 about 300 foot candles. Plants raised from germination on long 

 days showed high male sterility, some 50 percent of the anthers 

 being sterile; in addition, pistil development was excessive. Plants 

 that had received some short-day exposure before being returned 

 to long days, however, showed normal pistil development and 

 fully fertile anthers. Hence this plant, while grossly an LDP in 

 terms of mere flower initiation, is clearly an SLDP for normal 

 flower development. 



Chemical control of sex expression has been studied in a 

 variety of plants. The earliest clear-cut results with auxins (chiefly 

 naphthaleneacetic acid) were obtained on monoecious cucurbits 

 such as the cucumber, Cucttmis satimis, in which feminization is 

 promoted (see, for example, Laibach and Kribben, 1950). Subse- 

 quent work on other plants as well seems to bear out the 

 generalization that high auxin levels favor pistillate and reduce 

 staminate expression. As with other factors, such effects are not 

 confined to plants with unisexual flowers. The Silene work discussed 

 above also included studies of the effects of auxin application; 

 these, like continual exposure to long days, caused male sterility 

 and overdevelopment of the pistil. 



Other growth-regulating substances whose mechanism of action 

 may be related to that of auxins also affect sex expression. Maleic 

 hydrazide and 2,3,5-triiodobenzoic acid both may cause male 



