106 CARNEGIE INSTITUTION OF WASHINGTON. 



showed slight increase after 7 generations and a marked increase after 12 

 generations of selection. It now averages about double its original manifes- 

 tation of the character, an average approximately 15 times as great as the 

 present average for the low strains. The appearance of the polygons showing 

 the course of this selection experiment suggests that changes in manifestation 

 of the character are of the nature of mutations of smaller or larger degree. 



The studies in selection with Cladocera, the first of which was published 

 by the Institution (Carnegie Inst. Wash. Pub. No. 305), demonstrate that 

 in these parthenogenetic organisms genetic changes of the nature of muta- 

 tions may occur with relative frequency and, as regards a particular character, 

 with probably as great frequency as in most organisms reproducing bisexually. 



INHERITANCE OF SPECIAL TRAITS. 

 Flowering Plants. 



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

 Upland cotton and of their hybrids. — Investigations have been continued by 

 Dr. J. A. Harris and his collaborators along the lines discussed in earlier 

 reports. A comparison of Pima Egyptian and Meade and Acala Upland 

 cotton and the Fi hybrid has been completed for publication. A study of 

 several newly-imported Egyptian types with respect to osmotic concentra- 

 tion, specific electrical conductivity, hydrogen-ion concentration, and chloride 

 content has been begun. 



As at present conducted, these studies involve not merely the comparison 

 of genetically distinct types, but an investigation of the differences in their 

 relationship to the substratum. In addition to the Egyptian cottons, Sea 

 Island has been included in the work carried out in 1923, and some observa- 

 tions made on variant types of both Egyptian and Upland cotton. From the 

 standpoint of methods, the most important advance has been the addition 

 of the determination of the sulphate ion, improvements in the method of 

 determining the chlorine ion, and the rapid determination of reducing sugars. 

 These determinations make possible a more analytical consideration of the 

 variables to which osmotic concentration and electrical conductivity are due. 



The studies made in 1923 were limited to the Gila River Indian Reservation, 

 where facilities were afforded by the Cooperative Testing Station. In this 

 work Dr. Harris was assisted by Professor John V. Lawrence, Dr. G. O. 

 Burr, Mrs. John V. Lawrence, Mr. W. B. Sinclair, and Mr. Charles W. Crane. 

 The work in 1923 was mainly devoted to Pima Egyptian and Lone Star 

 Upland cotton and their Fi hybrids. Preparations for the investigation of 

 the F2 hybrid are under way. 



Genetical analysis of white seedlings of maize. — Dr. M. Demerec is con- 

 tinuing here, in cooperation with Professor R. A. Emerson, of Cornell Univer- 

 sity, certain experiments on the genetical analysis of white seedlings in maize 

 which he began while in Ithaca, New York. 



Variation and Correlation of Fecundity in the Domestic Fowl. 



These studies have gone forward steadily during the year, under th 

 direction of Dr. J. A. Harris. Further reports are in press, and considerabe 

 progress has been made towards completing a volume summarizing the results 

 of all the work. 



