18431862] KNIGHT'S LAW 253 



great principle of " Nature not lying," I fully expected that Letter 585 

 trees would be apt to be dioecious or monoecious (which, as 

 pollen has to be carried from flower to flower every time, 

 would favour a cross from another individual of the same 

 species), and so it seems to be in Britain and N. Zealand. 

 Nor can the fact be explained by certain families having this 

 structure and chancing to be trees, for the rule seems to hold 

 both in genera and families, as well as in species. 



I give you full permission to laugh your fill at this wild 

 speculation ; and I do not pretend but what it may be chance 

 which, in this case, has led me apparently right. But I repeat 

 that I feel sure that my doctrine has more probability than 

 at first it appears to have. If you had not asked, I should 

 not have written at such length, though I cannot give any of 

 my reasons. 



The Leguminosas are my greatest opposers ; yet if I were 

 to trust to observations on insects made during many years, 

 I should fully expect crosses to take place in them ; but I 

 cannot find that our garden varieties ever cross each other. 

 I do not ask you to take any trouble about it, but if you should 

 by chance come across any intelligent nurseryman, I wish you 

 would enquire whether they take any pains in raising the 

 varieties of papilionaceous plants apart to prevent crossing. 

 (I have seen a statement of naturally formed crossed Phaseoli 

 near N. York.) The worst is that nurserymen are apt to 

 attribute all varieties to crossing. 



Finally I incline to believe that every living being requires 

 an occasional cross with a distinct individual ; and as trees 

 from the mere multitude of flowers offer an obstacle to this, 

 I suspect this obstacle is counteracted by tendency to have 

 sexes separated. But I have forgotten to say that my maxi- 

 mum difficulty is trees having papilionaceous flowers : some 

 of them, I know, have their keel-petals expanded when ready 

 for fertilisation ; but Bentham does not believe that this is 

 general : nevertheless, on principle of nature not lying, I 

 suspect that this will turn out so, or that they are eminently 

 sought by bees dusted with pollen. Again I do not ask you 

 to take trouble, but if strolling under your Robinias when in 

 full flower, just look at stamens and pistils whether protruded 

 and whether bees visit them. I must just mention a fact 

 mentioned to me the other day by Sir W. Macarthur, a clever 



