Tricofyloits Half Races. 383 



can l)e isolated immediately; if it is not, no amount of 

 selection will bring it aliout. The experiments in whicli 

 isolation succeeded will be described in § 6; but the ex- 

 periments which failed fall into two groups, according 

 to whether it could be decided immediately, or not until 

 much later, that an intermediate race could not be raised. 

 In the former group fall those cultures in which there 

 was no progress at all, or so small a one that I had to 

 give them up after three or four generations. For if, 

 after this time, a proportion of no more than from 1 to 

 2 or at most 4% is reached, or if in the case of higher 

 proi)ortions the ratio fluctuates greatly but does not ex- 

 hibit a regular increase, how many years of work would 

 it take l)efore we can be certain that nothing can be at- 

 tained ? These briefer experiments will form the sub- 

 ject of this section. 



In the second group fall two cultures which I have 

 continued for a considerable time, namely Ainarantus 

 speciosus through nine generaiions and Scrophidaria no- 

 dosa through ten. Neither now leaves any hope of ever 

 becoming successful (see >^ 3) ; but, as I have already 

 said in the first part of this volume (p. 227), it is just 

 the experiments in selection that fail, which give us the 

 deepest insight into the nature of elementary characters. 



I shall now proceed to the description of my ex- 

 periments; and I shall confine myself to those which 

 were instituted with the express hope of breeding a 

 tricotylous intermediate race, and were continued f(^r 3 

 or 4 generations with this sole object in view, until it 

 l)ecame evident that only a half race was present. The 

 extent of the cultures varied greatly, according to the 

 importance which I attached to them at tlie l)cginning. 

 In the fir<^t place T shall deal witli Ocuothcra nihrinrnis. 



