88 REPORTS ON INVESTIGATIONS AND PROJECTS. 



that station to carry on his work here as Research Associate. At present 

 he is working to discover which of the sexual races of the mucors, provi- 

 sionally designated by the terms ( + ) and ( — ), is actually male and which 

 female. The effect of varying external conditions upon the sex, the form 

 and physiology of the individual races, and their influence in inheritance will 

 be tested. He reports that of the mucors he has under cultivation 8 her- 

 maphrodite species and the paired strains of some 22 dioecious species, be- 

 sides individual unmated races of a considerable number of other species. 



HEREDITY OF OTHER CHARACTERISTICS. 



Heredity of Flower and Foliage Colors. — Dr. Shull reports interesting 

 studies in two species. In Lychnis the announcement of the discovery of a 

 "dominant white" was premature, as the second hybrid generation proves 

 that this white was a recessive white which was mated to unsuspectedly im- 

 pure stock. The hopes expressed in the last report of being able to secure 

 purebred purple-flowered strains from the reddish series have been realized. 

 A "homozygous" or purebred "tinged white" strain has been produced ; a 

 number of different grades of greenness in foliage have appeared, indicating 

 distinct biotypes; and variegated forms have arisen whose inheritance is 

 being studied. The component color elements involved in the Shirley poppy 

 have been isolated and some colors have been produced which are not visible 

 in the original stock. 



Heredity of Pitcher-leaved Ash Trees. — In studies in heredity with plants, 

 garden or domesticated varieties have been largely employed and the char- 

 acters studied have largely arisen under culture. But this is quite natural, 

 since only the cultivated plants are best known ; however, it has been raised 

 as a criticism of modern studies. Studies are now being made by Dr. Shull 

 on a striking character that occurs in a group of ash trees found in the 

 forest near by, namely, the cornucopia-like folding of the terminal leaflet. 

 He has bred trees having this character to themselves and to "normals" and 

 has got from the first kind of cross some seedlings that already show the 

 foldings ; but none from the second kind of cross. 



The Aberrant Inheritance Ratio of Bursa. — In continuation of his studies 

 on this subject Dr. Shull finds that of the two hypotheses formulated to 

 account for the unexpected inheritance ratios in the second hybrid and later 

 generations of the cross between the flat capsuled and the elliptical capsuled 

 bursas, the first is confirmed, the other must be rejected. The triangular 

 capsule is independently produced by two different determiners, and the 

 theoretical ratios of 15: 1 in the F 2 generation and of 15: 1 and 3:1m the 

 F 3 generation are to be expected. The hypothesis of the relative inefficiency 

 of the heegeri type of fertilized egg is rendered untenable by the fact that 

 families have appeared with an excess of heegeri offspring. The deviations 

 from the expected ratio of 15:1 is accounted for on the hypothesis of a 

 selective fertilization producing the observed excess of triangular capsules. 

 The hypothesis is to be tested. 



