348 



SCIENCE 



[Vol. LV, No. 1422 



university year 1920 there were 1,505 students; 

 in the year 1921 there were 2,415, and at pres- 

 ent there are over 2,600, and there is every 

 prospect that the increase will continue. Pro- 

 vision for further development has been made 

 there by 175 professorships in the place of 90 

 chairs before the war. 



Claude Bukton Hutchison, professor of 

 plant breeding of Cornell University, has been 

 selected by the regents of the University of 

 California to head the activities of the branch 

 of the College of Agriculture at Davis and to 

 become professor of plant breeding. 



Dr. D. H. Dolley, professor of pathology at 

 the University of Missouri, has been appointed 

 director and professor of pathology in the 

 St. Louis University School of Medicine. Dr. 

 R. L. Thompson has resigned as director but 

 will continue in the department. 



Dr. H. R. Dean, professor of pathology and 

 pathological anatomy in the University of Man- 

 chester, has been appointed to the iiniversity 

 chair of bacteriology at the University of Lon- 

 don, tenable at University College Hospital 

 Medical School. 



DISCUSSION AND CORRESPOND- 

 ENCE 

 SELECTIVE FERTILIZATION AS AN INDI- 

 CATOR OF GERMINAL DIFFERENCES 



It has been argued from time to time that the 

 qualities which separate species are essentially 

 different in kind from the visible variations 

 which the geneticists are now busily describing 

 in terms of genes. The position of those who 

 take the affirmative side is fairly stated, I be- 

 lieve, in the following quotation from Bateson's 

 recent address before the American Association 

 for the Advancement of Science: 



Analysis [of the hereditary traits of animals 

 and plants] has revealed hosts of transferable 

 characters. Their combinations suffice to supply 

 in abundance series of types which might pass 

 for new species, and certainly would be so classed 

 if they were met with in nature. Yet critically 

 tested we find that tkey are not distinct species 

 and we have no reason to suppose that any accu- 

 mulations of characters of the same order would 

 culminate in the production of distinct species. 

 Specific differences therefore must be regarded as 



probably attaching to the base upon which these 

 transferables are implanted of which we know 

 absolutely nothing at all. Nothing that we have 

 witnessed in the contemporary world can colorably 

 be interpreted as providing the sort of evidence 

 required. 1 



At this time lack of knowledge concerning 

 the primary factors of evolution makes the 

 stand of the agnostic undoubtedly a safe one 

 and the one which may be the most conducive 

 to real progress in the end. At the same time 

 there is some evidence which should be con- 

 sidered in connection with the statements made 

 in the quotation. 



It has been shown conclusively in one spe- 

 cies that fertilization takes place less readily 

 when the gametes come from unlike forms than 

 when homogeneous unions are made. The dis- 

 crimination becomes more pronounced as the 

 germinal differences of the uniting individuals 

 are greater.- Maize is better material than 

 most plants to show this because of the large 

 number of seeds it produces with one applica- 

 tion of pollen, and because the source of the 

 pollen is soon apparent in the characters of 

 the immediately resulting seeds. Mixed pol- 

 linations carried out with this organism have 

 shown that the individual's own pollen, when 

 acting in competition with pollen from other 

 individuals of different constitution, is more 

 effective in accomplishing fertilization. 



When two different plants of similar type 

 are compared the selective action is small. For 

 example, when two varieties of maize having 

 the same size and form of plant, equal length 

 of growing season, similar seed shape and tex- 

 ture of endosperm and differing only in minor 

 details are tested, the inequality in fertilizing 

 power of the two kinds of pollen is slight 

 although significant. The small difference in 

 genetic make-up of these plants is also shown 

 by the fact that there is very little heterosis 

 exhibited in the increased weight of the crossed 

 seed compared to the self-fertilized seed. But 

 when a small-growing variety having non- 

 starchy endosperm is paired with a larger vari- 

 ety which differs markedly from it in habit of 

 growth, has starchy corneous seeds of very 



I Science, 1922, N. S. Vol. 55, pp. 59 and 60. 

 -' Biological Bulletin, 1920, Vol. 38, pp. 251-289. 



