DEPARTMENT OF EXPERIIVIENTAL EVOLUTION. Ill 



those reported on a year ago ; and a lot of wood-frog larvae reared in 

 the cave have developed very little pigment. But the most inter- 

 esting material is the amphipod Eucrangonyx gracilis, an almost 

 pigmentless form of which hves in caves in central Indiana, while 

 the normally pigmented form is abundant in the surface streams in 

 the same region. Series of these two forms have been placed both 

 in the cave and in the vivarium and interesting results are hoped for. 

 During the past winter a short time was spent in the cave region 

 in Indiana and numerous experiments were made on the light and 

 tactile reactions of the two forms of the above-mentioned amphipod. 

 In accord with the results of earlier experiments with an eyeless cave 

 isopod and its near outdoor relative, the cave amxphipod was found 

 to be less responsive to light and more responsive to tactile stimula- 

 tion than its outside relative. 



VARIOUS PROBLEMS IN HEREDITY. 



Inheritance in Shepherd's Purse, by George H. Shiill. 



The discovery by Neilsson-Ehle at Svalof of duplicate determiners, 

 for some of the characters of certain grains, has led to the discovery 

 of a similar sort in animals and plants and even in man. Dr. Shull 

 reports another case in a character upon which he has been at work 

 for some time and whose behavior appeared at first erratic. The 

 cultures of the present year have fully confirmed his view that there 

 are duplicate determiners, each of which, independently of the other, 

 is capable of producing the triangular type of capsule characteristic 

 of Bursa bursa-pastoris. In support of this proposition the following 

 facts have been demonstrated : 



(a) All individuals of the Fi families formed by crossing B. bursa- 

 pastoris with B. heegeri, have triangular capsules. 



(6) In all F2 families there is an approximation to the ratio of 

 15:1 between plants having triangular capsules and those having 

 top-shaped capsules. 



(c) When F2 families having triangular capsules are self-fertilized, 

 three kinds of F3 families are produced, namely, (1) those in which all 

 of the individuals have triangular capsules; (2) those in which the 

 individuals having the two kinds of capsules occur in the ratio 15: 1 ; 

 and (3) those in which the two kinds of plants appear in the ratio 3:1. 



(d) In the F4 the results differ according to the type of F3 family 

 from which plants of the dominant type are used for breeding; 



(1) The members of those F3 families which contained only plants 

 with triangular capsules produce only triangular capsules again; 



(2) when the parents are triangular-capsuled plants from an F3 

 family in which a 15: 1 ratio occurred, the F4 families fall into the 

 same three groups as the F3 famihes; (3) from the dominant indi- 



