feb., 1923] stout alternation of sexes 63 



Discussion 



The alternative loss of maleness and femaleness in the flowers of Cleome 

 spinosa and the recurring periodic changes in the sex of the flowers are to 

 be regarded as phenomena of internal and biogenetic regulation closely 

 related to those influences which determine the development of the plant 

 as a whole. 



It is, of course, well recognized that in plants as contrasted with animals 

 there is continually the formation of really new organs from a persistent 

 embryonic complex of cells and that this continues until the maturity and 

 death of the plant as a whole. Internal and biogenetic relations of corre- 

 lation and self -regulation, operating independently or in response to external 

 influences, are hence repeated successively in determining the character of 

 the new organs in the same fashion as they operate once for all in the animal. 

 When there is in addition a long flowering period which overlaps and is 

 coincident with the period of the most vigorous vegetative development, 

 as is the condition in this robust annual Cleome spinosa, the conditions are 

 most favorable for a study of the factors influencing the differentiation 

 of sex. 



The fact that the loss of sex organs in the flowers of the spider flower is 

 very decidedly one-sided and qualitative is of special significance. When 

 the stamens are aborted the pistil is as a rule functional, and in many cases 

 it is well developed ; when the pistil is aborted the stamens are often highly 

 developed and functional. Here, as is the rule in plants, intersexualism 

 does not lead to sterility of the plant or of a flower as a whole. Not a 

 flower was found in which the pistil and all the stamens were extremely 

 aborted, and rather rarely was the abortion of one sex accompanied by 

 the decided abortion of the other sex in the same flower. Abortion 

 of pistils was frequently accompanied by irregular abortion among the 

 various stamens of a flower, but the same irregularity in maleness was also 

 seen for flowers in which there was no abortion of the pistil (see the flowers 

 of fig. 4). While the expression of sex in at least half of the flowers of a 

 plant is decidedly one-sided and alternative, it is not mutually exclusive, 

 for on every plant many bisexual flowers are produced. 



It should be noted that the influences operate primarily and almost 

 discriminatingly on the organs of sex. The pedicels, sepals, and petals are 

 often uniformly well developed for all the types of flowers ; but undersized 

 flowers were to be seen (c of fig. 3, and d of fig. 4) in which the flower as a 

 whole is undersized. Such cases, if more general, would suggest a direct 

 relation to waning vigor and decreased food supply such as may be con- 

 sidered to be the direct cause of undersized flowers and of loss of sex in 

 gynomonoecious forms at the end of a period of bloom. That the conditions 

 are more intricate in Cleome is evident, for in a marked degree the extreme 

 variations in sex are independent of any other visible change and the various 

 grades of intersexes are present from the beginning of bloom. 



