Selective Breeding and Vegetative Propagation. 83 



Properly speaking these cases have no significance 

 for the theory of descent. But they are so much more 

 striking than the results of selection in seedplants that 

 they are often used as examples. 



If after extensive sowing, or after repeated selection 

 of any species one gets a single example with large 

 flowers or fruits or with any desirable character in an 

 exaggerated degree there are two possibilities. 



First one may be dealing with a seedplant, that is with 

 a species which can either be propagated only by seed, 

 or in which it is usual to propagate it in this way in 

 practice. 



Secondly, one may be dealing with a plant which is 

 capable of vegetative propagation whether by division 

 of the rhizom, by cuttings, by grafting, by tubers, or by 

 any of the other ways in which this may be effected. 



In the first case the seeds conform to the law of re- 

 gression. This was recognized by Vilmorin and after- 

 wards scientifically studied by Galton. If we regard 

 Galton's formula as generally true the mean of the 

 offspring deviates from the mean of the type in such a 

 way that it retains only a third of the deviation of the 

 parent. So that to produce a given advance in the whole 

 family we should have to sow seed from a plant which 

 had advanced three times as far. 



To make the meaning of this regression clear I will 

 select as an example a culture of Madia elegans. The 

 mean number of ray-florets on a flower head is 21. 

 and the other numbers are grouped round this in accord- 

 ance with Quetelet's law. In the 1892 crop of my ex- 

 periment the mean was 21 and the variation lay between 

 16-25 ; of these I chose 6 examples, each possessing 16-19 

 rays in the terminal head. From their seeds T obtained 



