182 HETEEOSTYLED TKIMORrHIC PLANTS. CHAP. IV. 



quite fertile with its own pollen when insects are ex- 

 cluded. The stigmas of 0. stricta and of another homo- 

 styled species, viz. 0. tropsBoloides, commonly stand on 

 a level with the upper anthers, and both these species 

 are likewise quite fertile when insects are excluded. 



With respect to 0. acetosella, Hildebrand says that in 

 all the many specimens examined by him the pistil 

 exceeded the longer stamens in length. I procured 

 1 08 flowers from the same number of plants growing in 

 three distant parts of England ; of these 86 had their 

 stigmas projecting considerably above, whilst 22 had 

 them nearly on a level with the upper anthers. In 

 one lot of 17 flowers from the same wood, the stigmas in 

 every flower projected fully as much above the upper 

 anthers as these stood above the lower anthers. So 

 that these plants might fairly be compared with the 

 long-styled form of a heterostyled species ; and I at 

 first thought that 0. acetosella was trimorphic. But 

 the case is one merely of great variability. The 

 pollen-grains from the two sets of anthers, as observed 

 by Hildebrand and myself, do not differ in diameter. 

 I fertilised twelve flowers on several plants with pol- 

 len from a distinct plant, choosing those with pistils 

 of a different length ; and 10 of these (i.e. 83 per cent.) 

 produced capsules, which contained on an average 7'9 

 seeds. Fourteen flowers were fertilised with their own 

 polleii, and 11 of these (i.e. 79 per cent.) yielded cap- 

 sules, containing a larger average of seed, namely 9'2. 

 These plants, therefore, in function show not the 

 least sign of being heterostyled. I may add that 18 

 flowers protected by a net were left to fertilise them- 

 selves, and only 10 of these (i.e. 55 per cent.) yielded 

 capsules, which contained on an average only 6*3 seeds. 

 So that the access of insects, or artificial aid in placing 

 pollen on the stigma, increases the fertility of the 



