426 Tricotylous Races. 



parent with the value of 56^0 flowered in a cage of metal 

 gauze. The values, calculated in the usual way from the 

 harvest, gave a good curve, whose mean was 72^0. The 

 lowest percentage of tricotyls was now 38%, the three 

 highest 83 — 83 and 89^0, that is to say, a very consider- 

 able advance. 



Atavistic seedlings of the same parent were also 

 planted out. but they naturally exhibited a somewhat 

 smaller advance. 



In the following year, 1898, I did not sow the seeds of 

 the plant with 89%, but from various considerations 

 those of one with 66%. The reason for this choice was 

 that the plant had flowered early and that the harvest 

 had been increased thereby. The parents with the higher 

 values had flowered too late or set too little seed, and it 

 would have been very dangerous to have continued the 

 experiment along this line. Moreover there was no 

 longer any particular interest in improving the race fur- 

 ther. The mean value has been lessened thereby to 

 about 40%, and the maximum to 74%. 



Cannabis sativa. I propose to deal now with two 

 cultures of dicEcious plants, Cannabis and Mercurialis. 

 In these cases self-fertilization is impossible; neverthe- 

 less the isolation of the intermediate races was effected 

 as easily and almost as quickly as in Oenothera. Without 

 doubt self-fertilization has in such experiments, when- 

 ever feasible, the high value which is usually assigned to 

 it ; but the experiments now to be described show that it 

 can often be dispensed with, as well. This result is very 

 important, because it makes isolation and selection pos- 

 sible in species in wdiich an artificial fertilization of every 

 single seed-parent would increase the labor bevond meas- 



