510 THE FERTILISATION OF FLOWERS. [PART III. 
pollen on both sides. This species is dimorphic, and in this respect 
it stands alone in its genus. The anthers stand in the one form 
on a level with the stigmas in the other, and there is the usual 
difference in the size of the pollen-grains. In long-styled flowers 
(Fig. 172, 1), most visitors touch the anthers with their heads, and 
the stigmas with the sides or ventral surfaces of thorax and abdo- 
men. ‘The converse takes place in the short-styled forms, so that 
legitimate fertilisation for the most part takes place, though neither 
illegitimate crossing nor fertilisation of a flower with its own pollen 
are quite prevented. 
The smaller visitors, ¢.g. Andrena nana, which creep about 
irregularly in the flower, may lead to self-fertilisation and legiti- 
mate or illegitimate crossing indifferently. 
Fic. 172.—Polygonum fagopyrum, L. 
1.—Long-styled, 2.—Short-styled flower, after removal of two segments of the perianth. 
Occasionally flowers occur on long-styled plants, in which the 
style is so much shorter than usual that the stigmas lie between 
the three inner stamens and get dusted by their pollen. 
Self-fertilisation is probably inoperative under ordinary circum- 
stances in the Buckwheat, but under altered conditions, if insect- 
visits decreased, it might easily come into play (cf. Darwin, 167, 
p. 113). 
The following insects were almost all collected by me on 
Buckwheat, one sunny day, in a large field near Salzkotten (June 
21, 1868), 
A. Hymenoptera—-(a) Apide: (1) Apis mellifica, L. $, very ab., s. and 
c.p., making fully nine-tenths of all the visitors ; (2) Bombus lapidarius, L. 
2%, s.; (3) Andrena fulvicrus, K. ¢ 2, ab., s. and c.p.; (4) A. dorsata, K. 
2; (5) A. pilipes, F. 9; (6) A. helvola, L. 9; (7) A. varians, Rossi, 9 ; (8) 
A. albicrus, K. 9; (9) A. Gwynana, K. 9; (10) A. nana, K. 9; (11) A. 
bicolor, F. (estiva, Sm.), ¢; (12) Sphecodes gibbus, L., Nos. 4—12, sucking 
only ; (b) Sphegide : (13) Pompilus trivialis, K1. ; (14) Cerceris labiata, F. 9 ; 
(15) C. nasuta, Dib. (C. quinquefasciata, Ross.), ¢, all s.; (c) Tenthredinide : 
