380 Origin of Each Species Considered Separately. 



duce three different forms, 0. scintillans, O. ohlonga, and 

 O. Laniarckiana even after it has been carefully fertilized 

 with its own pollen and the visits of insects have been 

 effectually excluded. The proportion in which O. scin- 

 tillans is reproduced is in some cases about 35-40 % and 

 in others about 70 %. 



Before we can estimate the effects of this incon- 

 stancy we must know what happens in subsequent gen- 

 erations. I shall afterwards give the details of some ex- 

 periments which show that the 0. ohlonga and 0. La- 

 marckiana thus produced are as constant as those given 

 off directly from the main stem of the Laniarckiana-isim- 

 ily. The scintillans on the other hand behave like their 

 parent, their offspring segregating in the same way. 



What will be the composition of the successive gen- 

 erations? We will suppose that the plants are self- 

 fertilized, that no selection takes place and we will put 

 the proportion of scintillans in each generation at about 

 one-third. And we will limit the extent of the genera- 

 tions to a thousand plants each. The contents of suc- 

 cessive generations will, then, obviously be :^ . 



Therefore in a batch of about 1000 plants all the 



scintillans would have died out after seven generations 



without the operation of any selective process. In the 



case before us however the process would be hastened 



^The xth generation will contain (Va)^ scintillans. 



