154 BOTANY 
Flies, on the other hand, appear to be specially 
attracted by yellow. Sunflowers will seldom be 
without one or more of these insects. Flowers that 
depend on the visits of night-flying isects are gener- 
ally white, as is the case with the clematis and many 
other New Zealand flowers. Their perfume, which 
arises only after sundown, is the means of attraction 
in the evening primrose and night-scented stock. At 
night, too, the kohuhu (Pittosporum tenwfolium), a 
common native shrub much used for hedges, diffuses a 
delicious perfume, doubtless for the same purpose, 
though the dark colour of its flowers affords no 
assistance to night-flying insects. 
Protection.—The petals, as well as the sepals, may 
serve to protect the essential inner parts of the flower, 
especially the pollen, after it has been shed from the 
anther. This protection may be permanent or tem- 
porary, in the latter ease arising merely as occasion 
requires. In the bean, the folded keel protects the 
pollen, in self-heal the arched roof, and in the poly- 
anthus the constricted tube of the corolla serve the 
same purpose. In the potato, temporary protection is 
afforded by the drooping of the flower when rain is 
threatening, while in the water lily the pollen is 
shielded from the dew by the nightly closing of the 
petals. Temperature plays an important part in the 
opening and closing of many flowers. On a cold frosty 
morning interesting experiments may be made with a 
crocus flowering in a pot. Left exposed to a temper- 
ature not exceeding 15° C., it remains unopened, but, 
if taken into a room heated to between 20° and 25° C., 
it will at once begin to unfold. The advantage of the 
protection thus afforded to the pollen against frost and 
snow is essential to a flower that matures so early in 
the spring. 
Light, too, exerts an important influence in con- 
nection with the opening and closing of flowers. 
