Tricot ylous Races Do Not Arise by Selection. 415 



412), successful throughout. Nevertheless an interme- 

 diate race has not arisen, either graduall)' or by means 

 of a sudden jump. The progress in the last two years was 

 more rapid than before as the result of increased strin- 

 gency of selection, without, how^ever, affording any in- 

 dication that the mean of 50% was likely soon to be 

 reached. 



Oenothera Bcrteriana. Besides the two cultures men- 

 tioned which were begun in the first years of my ex- 

 periments in selection, I have cultivated yet a third race 

 with the same object. This race was one in whicli the 

 intercrossing of the various individuals could always be 

 avoided. There is, however, no ground for fear that 

 occasional unavoidal^le crosses in Aniarantns and Scro- 

 pJi III aria had any considerable effect on the selection pro- 

 cess ; for both species must be fertilized almost entirely 

 with their own pollen on acount of the great number of 

 their flowers which are open at the same time ; and they 

 are, when thus fertilized, perfectly fertile as isolated in- 

 dividuals show. Moreover what is spoiled by crossing 

 is eliminated bv selection. 



But the evidence is more satisfactory if self-fertiliza- 

 tion can be insured. This occurs in Oenothera Bcrteriana. 

 Its flowers form perfectly normal fruits and seeds, when 

 the \isits of insects are excluded. I enclosed my plants 

 in a cage of fine metal gauze. Some years I have fer- 

 tilized them artificially in it ; but this is quite superfluous, 

 because when the flower withers the stigrna bends down- 

 wards and thus reaches the pollen. Tn the two last sum- 

 mers the cage was shut from the beginning of the flow- 

 ering period until the seed began to ripen. Nevertheless 

 they all produced fruits with scarcely an exception. These 

 fruits contained an abundance of seed, and a few from 



