DEPARTMENT OF GENETICS. 121 



different characters in the same individual, the parasitized D. pulex inter- 

 grades closely resembled the intergrade D. longispina. All of the D. pulex 

 intergrades that could be found were carefully cared for, but all were para- 

 sitized and died within a few days. A few other individuals of the same 

 material were also parasitized and yet possessed normal secondary sex- 

 character. The infection may have reached these individuals too late in 

 hfe to affect their secondary sex-characters. Inasmuch as all the intergrades 

 were parasitized, it is beUeved that the intergrade condition was the result 

 of parasitism. This has considerable theoretical interest. It is a case of an 

 apparently purely somatic effect which most strikingly resembles the effect 

 of genetic factors in other similar material. The general resemblance of the 

 parasitically produced intergrades of D. pulex and the genetically produced 

 intergrades of D. longispina is so striking that except for the species-character 

 differences and the presence of parasites in the former it is doubtful if we 

 could distinguish intergrades of the two classes." 



INHERITANCE OF SPECIAL TRAITS. 

 Flowering Plants. 



Rudbeckia. — Dr. Blakeslee has published "A chemical method of 

 distinguishing genetic types of yellow cones in Rudbeckia,' ' in the 

 Zeitschrift fiir induktive Abstammungs- und Vererbungslehre. He de- 

 scribes his discovery of the two strains of "yellow daisy" with a yellow 

 instead of a purple cone. These were indistinguishable in the field, 

 but dipped in alkali the flow^ers of one race turn black, the other red. 

 When black-yellow is self-pollinated, only black-yellow is produced; 

 when it is pollinated with ordinary purple heads all progeny are 

 purples in Fi, and in F2 purple and yellow appear in the proportion 

 of 3 : 1. The red-yellow^ behaves similarly. WTien the black-yellow 

 and red-3^ellow^ are crossed, the offspring are all purple in Fi, and 

 purple, red-yellow, and black-yellow^ again in F2. This work is prob- 

 ably the first wdiere a sharp cheixdcal distinction has been possible 

 between the genetic groups within one phenotype. 



Portulaca. — The development of the experiments with Datura has 

 made it necessary to reduce w^ork on Portulaca. Dr. Blakeslee has, 

 notwithstanding, secured important additional data regarding the 

 inheritance of color types in the flowxrs, and has found that dark 

 stigmas are dominant to light ones and dark pollen to light. The 

 frequent "somatic mutations" are, however, the chief point of interest. 

 Rather unexpectedly, nearly all of these mutations have arisen in 

 dominants that have arisen from reversion, and hence appeared first in 

 the heterozygous condition. Dr. Blakeslee reports that: 



"The possibihty of such mutations being reversible has been investigated. 

 For this purpose a pedigree was chosen showing a 1:2 :1 ratio for .yellow 

 and white petals, with the heterozygotes distinguishable from the homo- 

 zygous yellows by a less intense pigmentation. The parent of this pedigree 

 had arisen the previous year as a perichnal chimera from an inbred white 

 hne which shows frequent mutative striping with yellow. Of over 5,000 

 heterozygous yellow flowers examined. Miss Bergner, assisting Dr. Blakeslee, 



