Varietäten, Descendenz, Hybriden. 23 



tel}^ such an assumption necessitates an explanation of the origin 

 of atteniiata. 



The more general conclusions are following: 



1. Besides the genes (A, B, C, D) discovered by Shull, there 

 exists in Capsella a gene N, responsible for the narrow character 

 of the early leaves of certain forms. 



2. Absence of the gene N results in the formation of early 

 leaves of a "broad" character. 



3. The form designated arachnoidea is of hybrid origin, as are 

 the forms Setchelliana , Treleaseana and attenuata. 



4. X Capsella Biirsa-pastoris, arachnoidea is formed whenever 

 the plant is homozygotic for N, whatever the Constitution of the 

 remainder of the Zygote (BBNN, BbNN, bbNN), i. e., a homozygous 

 condition for the presence of a Single factor may overshadow the 

 influence of others. 



5. Homozygocity for a Single factor may be responsible for total, 

 or almost total, sterility. 



6. A knowledge of the early stages, as well as of the climax 

 leaves, is essential for the Classification of the phenotypes of Cap- 

 sella Bursa-pastoris. Jongmans. 



Hutcheson, T. B., Thirteen years of wheat selection. 

 (American Naturalist. XLVIII. p. 459—466. 1914.) 



In 1901 the Minnesota Agricultural Experiment Station planted 

 a number of varieties of wheat. Six of these varieties have been 

 grown continuously since that time and an effort has been made 

 to improve them by selection by the "centgener" method. This 

 centgener method consists in starting with individual plants, plan- 

 ting one hundred selected kerneis from each plant at equal depths 

 and at equal distances apart in separate plots. A plot of one hun- 

 dred plants is called a centgener. At harvest time five best plants 

 are selected from each centgener. From these five best plants from 

 five to ten of the best heads are selected and thrashed together. One 

 hundred of the largest and plumpest kerneis are then selected and 

 these are planted in the centgener test the next year. 



It is evident from the data presented in the tables of the paper 

 that there has been no permanent gain for thirteen years of selec- 

 tion either in yield per plant, height of plant, or shortening of neck- 

 lengths. The expected seasonal variations occur. 



The indications are present that from a practical breeder's 

 Standpoint permanent improvem.ent in pure lines in small grains, 

 if possible. is certainly not rapid or apt to be very marked. Thirteen 

 years of selection covers considerable time and expense, and, as 

 far as can be seen from the varieties reported in this paper, it has 

 resulted in no permanent improvement. This would suggest that 

 some other line of improvement must be sought It is probable that 

 much more rapid progress could be made by segregating pure lines 

 from mixed populations and combining the desirable characters of 

 these lines by hybridization. Jongmans. 



Jennings, H. S., Formulae for the results of i nbre eding. 

 (American Naturalist. XLVIII. p. 693-696. 1914.) 



For purposes of comparison the writer has worked out from 

 Pearl's data the general formula for the rate at which organisms 



