Chap. III. POLYGONUM FAGOPYEUM. 113 



heads yielded on an average 7 ■ 50 seeds per head ; 

 whereas the seven illegitimately fertilised heads 

 yielded less than half the number, or on an average 

 only 3 • 28 seeds. The legitimately crossed seeds from 

 the long-styled flowers were finer than those from the 

 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 mis- 

 taken in supposing that the long-styled flowers cannot 

 spontaneously fertilise 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. MuUer in his interesting description of several 



' Die Befruohtuug,' &o., p. 175, and ' Nature,' Jan. 1, 1874, p. 166. 



