58 AMERICAN JOURNAL OF BOTANY [Vol. 10, 



differentiation has been partly achieved. This often results in a more or 

 less complete sexual impotence or sterilization, a condition which has 

 naturally been very generally regarded as abnormal and pathological. This 

 is, however, not the case in those species of plants which are prevailingly 

 dioecious or monoecious, for here, as well shown in the muskmelons, there 

 is a tendency to produce flowers that are fully functional as hermaphrodites. 



Whether, however, intersexualism results in complete sterility, as it 

 frequently does in dioecious animals, or in one-sided sterility, as is the rule 

 in hermaphroditic plants, the physiological basis for these variations in sex 

 is to be regarded as most fundamental in the determination and expression 

 of sex. 



It is, furthermore, to be recognized that the mixture of sexes, with 

 blending and changes in the character of the organs, often results in a wide 

 range of variation in the morphological character of the different sex organs 

 produced by a single individual. In many plants, the flowers on a single 

 individual may be staminate, pistillate, and hermaphroditic, with also many 

 intergrading types, thus exhibiting many grades of sexual impotence with 

 marked differences in the ability to produce fruit. 



These cases of partial variability in sex are of special interest, for here 

 the various conditions of alternative impotence with corresponding irregu- 

 larities in the production of fruit are all seen among the flowers of a single 

 individual. In such cases there is also opportunity to observe whether the 

 variations are irregular and sporadic or whether they are related to a 

 definite period in development or are otherwise periodic. It is with special 

 reference to these questions that the changes in the character of the flowers 

 of Cleome spinosa L. are here reported as decidedly alternative and re- 

 peatedly cyclic, resulting in the intermittent production of fruit. 



Observations on Cleome spinosa 



This species is most favorable material for a study of variation in the 

 sex of flowers in relation to the development of the plant as a whole. It 

 has long been known as having mixed flowers, yet the species has not 

 become dioecious. All the individuals of the species are apparently quite 

 alike in respect to the general range of variations in the sex of the flowers. 

 The species is a quick-growing herbaceous annual. The first flowers open 

 on the main raceme when the plant is relatively small — about two feet tall 

 — and while the lateral branches are scarcely visible. The main raceme 

 continues to elongate, producing flowers daily, often for a period of from 

 eight to twelve weeks. Meanwhile a dozen or more lateral branches develop, 

 and these may in turn branch. All the branches grow rapidly and produce 

 flowers in abundance. When autumn arrives, well-grown plants are five 

 or more feet tall with a spread of branches of as many feet in diameter. 

 There has been a long period of bloom, often covering as many as ninety 

 days, and this has been for the most part coincident with the period of 



