DEPARTMENT OF EXPERIMENTAL EVOLUTION. 131 



THE INHERITANCE OF GERMINAL PECULIARITIES. 

 GENETICAL CONSTITUTION OF RUDBECKIA. 



Dr. Blakeslee has brought to this Station the investigation of varia- 

 bihty and heredity in the yellow daisy {Rudbeckia hirta), which he has 

 been making for several years ; this year he had under cultivation over 

 15,000 pedigree plants. He states: 



"Variations in the following characters have been found in wild plants: 

 Absence of rays and their presence in rather definite numbers from 8 to 30 

 and to perfectly double forms; mdth of rays; diameter of head from 1 to 5| 

 inches; color of rays from pale straw color to deep orange; relative intensity 

 of color in inner half of ray forming a lighter or darker ring; different intensi- 

 ties of mahogany color at base of ray on upper side; mahogany on under side 

 of ray; constriction of ray at tip, at middle, or at base — ^those constricted at 

 tip, either rolled in or rolled out to give the "cactus" type seen in dahlias — 

 those constricted at base without change in color or characterized by lighter 

 color or by presence of black pigment on constricted areas; transformation of 

 rays into tubes, giving 'quilled' type; the position of rays, bending upward, 

 horizontal, reflexed, straight, or variously twisted; the shape and size of disk; 

 the color of disk, from yellomsh green through several grades of purple to 

 almost black; vegetative characters, such as height, branching, size and shape 

 of leaf, fasciations, etc. 



"Evidence from the distribution of the variants in nature and from their 

 reappearance in sowings from open-pollinated heads shows that most if not 

 all of these variations are inherited. Certain of these characters appear to be 

 inherited in simple Islendelian manner; giving 3 : 1 ratios in the F2 generation. 

 Thus basal ' mahogany ' on the ray acts as a dominant, while a type of redden- 

 ing of the back and base of the ray v/hich I call ' chocolate ' acts as a recessive. 

 In both, however, pattern factors undoubtedly exist and are responsible for 

 the extreme variability in arrangement and intensity of the pigment. 



"One character, the presence of yellow in place of the normal purple in the 

 cone, has proven of considerable interest. I have obtained this variation from 

 several different localities. The peculiarity seems to be inherited as a simple 

 recessive. The fact, however, that the yellow-coned plants A crossed with B, 

 B with C, or C wdth A all produce purple-coned offspring shows that the yellow- 

 coned forms are not alike genetically. That they differ chemically is indicated 

 by treatment vnih KOH when the cone flowers of A turn black and those of 

 B and C turn bright crimson. Since seedlings that are destined to produce 

 3^ellow cones have no red pigment in their stems, it should be possible to save 

 considerable time by selection in the seed-pans, and my plans therefore are 

 to make a more intensive study of this character the coming season. 



"We have some 12,000 plants of the jimson weed {Datura slramonium) 

 under cultivation. Two mutations appeared in our cultures last year which 

 are being studied. The first is characterized by a globose capsule and broad 

 leaves and is apparently a recessive. The second has spineless capsules, slit 

 corollas, and lacerated leaves, and is apparently a dominant. The Daturas 

 have not yet been recorded this year, and it is therefore not possible to report 

 upon the behavior of these tj'pes in crosses nor of others that are appearing. 



"Among other problems under investigation may be mentioned inheritance 

 of self-sterility in Rudbeckia, Helianthus, and Verbena, parthenocarpy in 

 cucumbers, chemical and physical differences between the sexes in dioecious 

 plants, the annual habit in beets, various characters in Geodetia, Clarkia, 

 Portidaca, Fraxirms, Betula, Morus, Populus, and Salix." 



