§38 6- Vererbungslehre. 



characters in the potato, with an account of the metliods eraployed. The fol- 

 lowing are the chief results. Sterility of the authers behaves as a simple do- 

 minant to fertility, lut in some families spontaneous sterility appeared where 

 the parents were fertile. Usually however fertile plants cursed together gave 

 only fertile; sterile and fertile gave either only sterile, or equality of sterile 

 and fertile if the sterile parent is heterozygous. Most characters of the lea- 

 ves are not sufficiently definite for Mendelian analysis, but a peculiar twist 

 in the leaf, found in one variety, is a simple recessive. Some other charac- 

 ters of shape and texture probably segregate in Mendelian fashion. The shape 

 of the tuber appears at first very variable and inconstant, but by isolation of 

 types which can be pure-bred strict Classification is quite possible. If then 

 appears that length of tuber is dominant to roundness, the heterozygotes usu- 

 ally however being somewhat intermediate. In the shape of the 'eyes', depth 

 is dominant to shallowness, but heterocygotes may have shallower eyes than 

 homozygous deep-eyed tubers. In colour, potato tubers are purple, red, or 

 white, but even in white-tubered plants some red pigment occurs in the shrots. 

 White breeds true, and is recessive to colour. With regard to the relations 

 of the coloured forms, from a number of experiments (fully described and 

 illustrated with a coloured plate) it is concluded (1) that while colour may 

 be present in the stem to any degree, a special 'developer' factor (1) is ne- 

 cessary for its appearance in the tuber; (2) that redness is dependent on a 

 separate factor (R); (3) that purple is dependent on a third factor (P), and 

 (4) that purple colour cannot appear except in the presence of all three fac- 

 tors PRD. The depth of the reduess may depend on whether R or D are 

 homozygous or heterozygous. 



In addition to work with domestic varieties, experiments were made with 

 Solanum e tuberosum, of which a füll description is given. It has a diffe- 

 rent foliage, and for 20 years, during which attempts to raise seed from it 

 have failed, it has been quite immune to disease (Phytophthora). In 1908 

 however it set seed in abundance, and from that time onwards the plants ob- 

 tained from tubers have been infested with disease. Among the seedlings 

 about three were diseased to one immune, suggesting that immunity may here, 

 as in wheat, be a Mendelian character. The tubers are white (sometimes 

 tinged with purple) , rather round in shape , with shallow eyes. Seedlings 

 from self-fertilised plants included a mixture of longs and rounds and of 

 shallow and deep eyes. Hence in this species the dominance of these charac- 

 ters is reversed. In colour they gave a mixture of white and deep purple, 

 again reversing the dominance observed in domestic varieties. Crossed with 

 domestic varieties the white of etuberosum is also dominant. It is possible 

 that S. etuberosum is a hybrid; its origin is unknown. 



Doncaster (Cambridge). 

 1808) KeeMe, F. and C. Pellew (University College, Reading), The Mode 



of Inheritance of Stature and of Time of Flowering in Peas 



(Pisum sativum). 



(Journ. of Genetics 1,1. p. 47—56. 1910.) 

 The authors set out to investigate the inheritance of time of flowering 

 in peas, but finding it connected with morphological characters, they describe 

 the inheritance of the latter first. In stature Peas may be classified into 

 tall, dwarf, and half-dwarf races. On crossing two half-dwarf races, only talls 

 were obtained. It was found that one of the half-dwarf parents had thick 

 stems and short internodes, the other thin stems and long internodes. The 

 Fj plants had thick stems and long internodes, whence it is inferred that 

 these two characters are dominant over thin stem and short internodes. F 2 



