D - F. JONES. 



thera Lamarckiana. He interprets the result as due to a selective 

 action between gametes carrying different factors. In this case 

 as well as in the preceding experiments with Melandrium two 

 kinds of gametes were produced by the same individual and 

 presumably they were alike in respect to their cytoplasmic cover- 

 ing, differing only within the nucleus. In the case of Zea, 

 Lycopersicinn, Gossypium, and CEnothera Lamarckiana polli- 

 nated by gigas, the gametes came from different individuals of 

 unlike germinal construction and therefore differed both in nuclear 

 content and enveloping cytoplasm. The two manifestations of 

 selective fertilization may be unrelated. On the other hand it 

 is not unlikely that they may have something in common. 



The discrimination which works against the bringing together 

 of individuals of unlike germplasm has been demonstrated by 

 representatives of four distinct orders in the two main classes of 

 angiosperms. In its effect it is comparable to the assortative 

 mating of animals from the lowest to the highest. The predilec- 

 tion for the bringing together of like with like is more evident 

 as the germinal differences increase. There is thus exhibited a 

 tendency which when carried far enough may erect an impassable 

 physiological barrier between different groups that were once 

 compatible. It is an indication that sterility between species is 

 the result of the accumulation of genetic differences, however these 

 differences may arise. 



LITERATURE CITED. 

 Balls, W. L. 



'19 The Cotton Plant in Egypt. London. 

 Correns, C. 



'20 Eine gegluckte verschiebung des geschlechtverhaltnisses. Natur u. 



Technick, Vol. 2, pp. 65-71. 

 Heribert-Nilsson, N. 



'20 Zuwachsgeschwindigkeit der Pollenschlaiiche und gestorte Mendelzahlen 



bei Oenothera Lamarckiana. Hereditas, Vol. I, pp. 4 l -&7- 

 Jones, D. F. 



'20 Selective Fertilization in Pollen Mixtures. BIOLOGICAL BULLETIN, Vol. 



38, pp. 251-289. 

 Miller, E. C. 



'19 Development of the Pistillate Spikelet and Fertilization in Zea Mays L. 

 Journal Agricultural Research, Vol. 18, pp. 255-266. 



