2'3i THE STRUCTURE OF FLOWERS. 



tion, it will be as well to consider certain significant facts 

 which may help us in ascertaining the cause of their present 

 diclinism. 



"Hildebrand has shown," writes Mr. Darwin, " that with 

 hermaphrodite plants which are strongly protandrous the 

 stamens in the flowers which open first sometimes abort, . . , 

 Conversely the pistils in the flowers which open last sometimes 

 abort." Similarly Gartner observed that "if the anthers on a 

 plant are contabescent (and when this occurs it is always 

 at a very early period of growtli) the female organs are 

 sometimes precociously developed." * 



A reason for this is that, on the one hand, since a higher 

 temperaturn is correlated with protandry, the first flowers open 

 when the optimum temperature has not arisen ; so that the 

 stamens are checked, a cooler temperature being less inimical 

 to the development of the gynoecium. On the other hand, 

 the last flowers of the seasoji are produced when the vital 

 energy is waning, and although the flowers may expand, they 

 are too feeble to develop the pistil. 



Now exactly the converse may occur; thus Mr. W. G. 

 Smith called attention f to the seemingly unobserved fact 

 that Euphorbia amygdaloides always bea7\s terminal male 

 flowers alone at first, and subsequently the two sexes together 

 on lower lateral " flowers." This agrees with Castanea 

 Americana,^ as noticed by Mr. Median, In these two cases, 



* Forms of Floivers, p. 283. I hardly think this can be always the 

 case ; for, of Vines growing side by side, some "will occasionally have 

 the anthers utterly devoid of sound pollen, but with the pistil normal ; 

 while others will be entirely hermaphrodite with no sign of contabescence. 

 I have examined such, supplied to me by Mr. Barron from the gardens 

 of tiie Royal Horticultural Society at Chiswick. The cause is at present 

 veiy obscure. 



t Joiirn. ofBot., 1864, p. 196. 



X Proc. Acad. N. Sci. of Philadel., 1873, p. 290. 



