CHAP. IV. OXALIS, OTHER SPECIES OP 179 



which is the same thing, the greater the distance of 

 the stigma from the an,thers, the pollen of which is 

 used for fertilisation, the less fertile is the union, 

 whether judged by the proportion of flowers which 

 set capsules, or by the average number of seeds per 

 capsule. The rule cannot be explained in this case 

 any more than in that of Lythrum, by supposing 

 that wherever there is greater liability to self-fertilisa- 

 tion, this is checked by the union being rendered more 

 sterile ; for exactly the reverse occurs, the liability to 

 self-fertilisation being greatest in the unions between 

 the pistils and stamens which approach each other the 

 nearest, and these are the more fertile. I may add 

 that I also possessed some long-styled plants of this 

 species : one was covered by a net, and it set sponta- 

 neously a few capsules, though extremely few com- 

 pared with those produced by a plant growing by 

 itself, but exposed to the visits of bees. 



With most of the species of Oxalis the short-styled 

 form seems to be the most sterile of the three forms, 

 when these are illegitimately fertilised ; and I will add 

 two other cases to those already given. I fertilised 

 29 short-styled flowers of 0. compressa with pollen from 

 their own two sets of stamens (the pollen-grains of 

 which differ in diameter as 100 and 83), and not one 

 produced a capsule. I formerly cultivated during 

 several years the short-styled form of a species pur- 

 chased under the name of 0. Bowii (but I have some 

 doubts whether it was rightly named), and fertilised 

 many flowers with their own two kinds of pollen, 

 which differ in diameter in the usual manner, but 

 never got a single seed. On the other hand, Hilde- 

 brand says that the short-styled form of 0. Deppei, 

 growing by itself, yields plenty of seed ; but it is not 

 positively known that this species is heterostyled ; and 



