PART III. | THE MECHANISMS OF FLOWERS. 513 
eight stamens. The five which are constantly present alternate 
with the parts of the perianth ; the other three stand opposite to 
the parts of the perianth. At the base of each perianth-segment 
is a nectary, secreting very scanty honey, which remains in a 
moist adhesive layer. The ovary is generally bilateral, bearing 
a style which divides into two branches, each bearing a stigmatic 
knob; but three stigmatic branches often occur. Anthers and 
stigmas ripen together and stand at the same level. The flower 
expands until the perianth forms an almost hemispherical cup, 
and the five stamens alternating with the perianth-segments 
spread out as far as the perianth allows. The stigmas are, there- 
fore, seldom or never touched by these stamens, but the other 
three stamens, when present, bend towards the middle of the 
flower and come in contact with the stigmas. Now although, as in 
Fic. 174.—Polygonum Persicaria, L. 
1..—Flower with five stamens. 
2.—Pistil. 
8.—Flower with seven stamens. 
a, five outer anthers; a’, inner anthers; a*, rudimentary filament; 
ov, ovary ; st, stigma; mn, nectary. 
P. fagopyrum, the five outer anthers shed their pollen inwards and 
the three others outwards, self-fertilisation takes place regularly 
in all flowers with more than five stamens, since the anthers 
dehisce so widely as to be covered with pollen all round. Whether 
flowers with only five stamens fertilise themselves in absence of 
insects I cannot say from direct observation; but they probably 
do so, as almost all the flowers of P. Persicaria develop seed, in 
spite of the scanty insect-visits. The flowers, as I have often 
seen, remain expanded even in rain, and self-fertilisation in flowers 
with five stamens can only take place at the end of the flowering 
period, when the perianth closes up and brings stigmas and 
stamens into contact. 
The small size of the flower causes every insect that inserts 
its head to touch one or two stamens and a stigma. If the insect 
thrusts its proboscis once into each flower, cross-fertilisation. must 
LL 
