78 



Siiddoi .Ippcarcnicc and Constancy. 



once in a million) can not be excluded. The object of 

 experimentation cannot therefore be to demonstrate ab- 

 solute constancy. The best i)lan usually is to be content 

 with a few hundred individuals ; it is even often impos- 

 sible to get sufficient seed for more. Experiments on a 

 smaller scale should only serve to confirm the results ob- 

 tained in other cases; but even if they only do this they 

 are, in my opinion, by no means without value. 



Fig. 7. Bidcns tripartito. Type without ray florets. 



The nearest that we can get to demonstration of ab- 

 solute constancy is to make observations on races which 

 grow in vast quantities in certain districts and are never- 

 theless true to their type. In these cases the constancy 

 is so striking as to induce many systematists to regard 

 the form as a species. Amongst the better known ex- 



