PART III. | THE MECHANISMS OF FLOWERS. 515 
374, POLYGONUM AVICULARE, L.—The tiny flowers, scarcely 
2} mm, in diameter, are solitary, and therefore very inconspicuous ; 
they are odourless and show no honey, and are very rarely visited 
by insects. They always fertilise themselves, and every flower 
produces seed. . 
The number and arrangement of the floral organs is as in P. 
Jagopyrum. ‘The five segments of the perianth, which have the 
function of a corolla in P. fagopyrum, serve chiefly as a calyx (ie. 
a protective covering for the reproductive organs) in P. aviculare ; 
their lower parts are green, and only their extremities, which are 
white or red, play the part of a corolla in rendering the flower 
conspicuous. ‘The five stamens alternating with the parts of the 
perianth, which bend outwards, and the other three which curve in 
to the centre till their anthers stand immediately over the three 
Fic. 176.—Polygonum aviculare, 1. 
1.—Flower, from above. I 
2.—Ditto, in side-view, after removal of the two anterior parts of the perianth and of half the 
stamens. 
a, the five outer, a’, the three inner anthers ; ov, ovary; st, stigma, 
stigmas, have fleshy thickenings at their bases; but I have never 
succeeded in finding drops of honey. If the flower really secretes 
no honey, it can only have attractions for pollen-eating flies and 
pollen-collecting bees. In any case, from the simultaneous 
development of the male and female organs, and from the situ- 
ation of the three inner anthers over the stigmas, an insect-visitor 
must lead to self-fertilisation as easily as to cross-fertilisation. I 
had often watched this plant in vain, but at length on a very hot 
sunny day in August, 1871, I saw several insects visit it. They 
were several specimens of three small Syrphide, viz. Ascia poda- 
grica, F., Syritta pipiens, L., and Melithreptus menthastri, L. I 
came to the conclusion, by close observation, that Syritta pipiens 
was not only feeding on pollen, but was thrusting its proboscis 
into the base of the flower, as if to suck honey; it was therefore 
either sucking in vain, or licking a very thin layer of honey. 
LL 2 
