82 REPORTS ON inve;stigations and projects. 



depauperate inbred strain represents a "pure line." If this is so, then cross- 

 fertilization within the limits of the same pure-bred family ought not to 

 result in the increased vigor that cross-fertilization at random does. Now, 

 comparisons made between the effect of self-fertilization and crossing within 

 the limits of the same pure-bred family and within the same Fi showed in 

 each case a very slight difference in favor of the crosses. This difference 

 was so slight that the belief is entertained that it was due wholly to the fact 

 that some of the families used were not yet completely homozygous, but 

 there are other possibilities and these are being investigated. The Fi hybrids 

 between self-fertilized strains yielded on the average 68.07 bushels per 

 acre as compared with only 44.62 bushels yielded by the corresponding Fg 

 families, a fact of great potential consequence to the practical grower. The 

 conclusions derived from these investigations and published in 1908 have 

 been still further strengthened by these results. These conclusions are (a) 

 that the plants in an ordinary field of corn are generally very complex hy- 

 brids representing the combination of numerous elementary species or bio- 

 types; (b) that none of these pure biotypes is sufficiently vigorous to be 

 profitably grown in the pure state; (c) that the high physiological vigor of 

 the ordinary maize-plant is the result of a stimulating effect produced by the 

 union of unlike elements from the two parents; (d) that self-fertilization 

 decreases the vigor by gradually reducing the strain to a pure-bred state, 

 and not because there is any injury produced by self-fertilization or inbreed- 

 ing per sc. Comparisons are now being extended to the third and later gen- 

 erations, and tests are also being made to determine the effect of combining 

 a number of dift'erent pure-bred strains into a single hybrid strain. 



VARIATION AND MUTATION IN EVENING PRIMROSES. 



Since the beginning of our work we have continued the studies of the 

 evening primroses along th.e lines of Professor de Vries's work and with seed 

 largely derived from his cultures. In the past year the particular directions 

 of study, by Dr. Shull, have been the effects of cross and self fertilization. 

 Families have been grown from seeds of a number of new forms which 

 originated in the cultures of the preceding year. Some of these progenies 

 have bred true to their new characters, others have split up into several 

 types, and some have seemingly returned to typical Oenothera lamarckiana. 

 Reciprocal crosses have been made among several biotypes of O. cruciata, 

 and between each of these biotypes and O. lamarckiana. 



THE THEORY OE PURE LINES. 



This is quite the most hotly discussed of all topics in heredity to-day: 

 Does selection proceed by the isolation of minute units or by shoving the 

 character along a sliding scale ? It is not clear whether there is any real con- 

 trast between these views, since if the steps of a flight be taken fine enough 

 they will approach as close as possible to an inclined plane. Dr. Harris has 



