108 CARNEGIE INSTITUTION OF W.4SHINGT0N. 



that the sexual phenomena have been experimentally controlled, may now be 

 added a new line of experimental evidence. 



"Were there an internal sexual cycle one should expect Cladocera, because 

 of the working of the internal factor, to become more and more prone to 

 manifest sexuality as parthenogenesis continues. Experiments in control 

 of male production, using females from stock long subjected to partheno- 

 genesis in comparison with females just hatched from sexual eggs or having 

 descended by parthenogenesis for only one to seven generations, showed that 

 the stock which had recently gone through sexual reproduction produced males 

 just as freely as stock which had been exclusively parthenogenetic for 300 

 generations." 



Selection of Sex Intergrades in Daphnia. 



Continuing the experiments reported last year. Dr. Banta has, with the 

 assistance of Mr. George G. Snider, obtained from the selection of the sex- 

 intergrade stock of Daphnia longispina a mass of data which indicate that the 

 degree of sex-intergradeness is clearly inherited, that its inheritance is de- 

 pendent upon a single mutable factor (or several factors), and that genetic 

 change is rather frequent, though not equally frequent in all strains of this 



stock. 



Sex in the Mucor Cunninghamella. 



The study of the sexual condition in the mucor genus Cunninghamella has 

 been brought to completion by Dr. Blakeslee. The results of making con- 

 trast tests between more than 200 races from 4 different species offer no 

 evidence for an exception to the rule of a strict sexual dimorphism in this 

 genus. Similar studies on the intraspecific sexual reactions in some 30 different 

 species of other genera as well as study of the intraspecific reactions between 

 the sexual races of these different species strongly indicate that there is a 

 common fundamental something peculiar to each of the two sexes throughout 

 the whole group of the mucors. 



INHERITANCE OF SPECIAL TRAITS. 

 Flowering Plants. 



The physico-chemical properties of the leaf-tissue fluids of Egyptian and 

 Upland cotton and of their hybrids. — Genetic work has been largely confined 

 in the past to the visible morphological characteristics of organisms, such as 

 form and color. The possibility of studying the genetics of certain of the 

 biophysical and biochemical peculiarities has been opened up by the demon- 

 stration that Egyptian and Upland cottons, which hybridize freely, differ 

 in certain of these characteristics, such as osmotic concentration, specific 

 electrical conductivity, and hydrogen-ion concentration in their leaf-tissue 

 fluids. 



This demonstration was made by Dr. J. A. Harris in studies carried out 

 by courtesy of the U. S. Department of Agriculture at the Cooperative Testing 

 Station on the Gila River Indian Reservation at Sacaton, Arizona, in 1920 

 and 1921. An investigation of the sap properties of the Fi hybrid between 

 Egyptian and Upland cotton, carried out simultaneously with the above 

 investigations of the differentiation of the two forms, shows that the leaf- 

 tissue fluids of the hybrids are characterized by a lower osmotic concentra- 



