CHAP. III. PULMONARIA ANGUSTIPOLIA. 109 



when illegitimately fertilised; and I was thus led to 

 attend carefully to the degree of self-fertility of the 

 short-styled plants. A plant belonging to this form and 

 covered by the net bore 28 flowers besides those which 

 had been artificially fertilised, and of all these only 

 two produced a fruit each including a single seed. This 

 high degree of self-sterility no doubt depended merely 

 on the stigmas not receiving any pollen or not a suffi- 

 cient quantity. For after carefully covering all the 

 long-styled plants in my garden, several short-styled 

 plants were left exposed to the visits of humble-bees, 

 and their stigmas will thus have received plenty of 

 short-styled pollen; and now about half the flowers, 

 v thus illegitimately fertilised set fruit. I judge of this 

 proportion partly from estimation and partly from 

 having examined three large branches, which had borne 

 31 flowers, and these produced 16 fruits. Of the fruits 

 produced 233 were collected (many being left un- 

 gathered), and these included on an average 1.82 seed. 

 No less than 16 out of the 233 fruits included the high- 

 est possible number of seeds, namely 4, and 31 included 

 3 seeds. So we see how highly fertile these short- 

 styled plants were when illegitimately fertilised with 

 their own-form pollen by the aid of bees. 



The great difference in the fertility of the long-. and 

 short-styled flowers, when both are illegitimately fer- 

 tilised, is a unique case, as far as I have observed, with 

 heterostyled plants. The long-styled flowers when thus 

 fertilised are utterly barren, whilst about half of the 

 short-styled ones produce capsules, and these include a 

 little above two-thirds of the number of seeds yielded 

 by them when legitimately fertilised. The sterility of 

 the illegitimately fertilised long-styled flowers is prob- 

 ably increased by the deteriorated condition of their 

 pollen; nevertheless this pollen was highly efficient 



