CHAP. III. POLYGONUM FAGOPYRTJM. H3 



illegitimately fertilised flowers on the same plants, in 

 the ratio of 100 to 82, as shown by the weights of an 

 equal number. 



About a dozen plants, including both forms, were 

 protected under nets, and early in the season they pro- 

 duced spontaneously hardly any seeds, though at this 

 period the artificially fertilised flowers produced an 

 abundance; but it is a remarkable fact that later in 

 the season, during September, both forms became highly 

 self-fertile. They did not, however, produce so many 

 seeds as some neighbouring uncovered plants which 

 were visited by insects. Therefore the flowers of neither 

 form, when left to fertilise themselves late in the season 

 without the aid of insects, are nearly so sterile as most 

 other heterostyled plants. A large number of insects, 

 namely, 41 kinds as observed by H. Miiller,* visit the 

 flowers for the sake of the eight drops of nectar. He 

 infers from the structure of the flowers that insects 

 would be apt to fertilise them both illegitimately as 

 well as legitimately; but he is mistaken in supposing 

 that the long-styled flowers cannot spontaneously fer- 

 tilise themselves. 



Differently to what occurs in the other genera 

 hitherto noticed, Polygonum, though a very large 

 genus, contains, as far as is at present known, only a 

 single heterostyled species, namely, the present one. 

 H. Miiller, in his interesting description of several 

 other species, shows that P. bistorta is so strongly pro- 

 terandrous (the anthers generally falling off before the 

 stigmas are mature) that the flowers must be cross- 

 fertilised by the many insects which visit them. Other 

 species bear much less conspicuous flowers which se- 

 crete little or no nectar, and consequently are rarely 



* 'Die Befruchtung,' &c., p. 175, and 'Nature,' January 1, 1874, 

 p. 166. 



