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92 PLANTS AND ANIMALS 
strikingly irregular blossom, with the upper sepal 
arching over into a great hood protecting the rest of 
the flower. In such irregular flowers the essential 
parts—the pollen-producing and pollen-receiving por- 
tions, or stamens and stigma—also alter their position 
and form, and are so placed that an insect, visiting the 
flower to obtain nectar (which is generally stored at 
the back, well out of the way), must of necessity 
receive pollen on its body, and probably deposit pollen 
on the stigma. To describe the variety and ingenuity 
of these devices as found in different flowers might 
well occupy several chapters, and only one or two 
examples can be quoted here; familiar wild flowers are 
chosen, and the reader should examine them for him- 
self to understand their structure. In the well-known 
Pea type, one great petal arches over the flower; two 
narrow ones stand one on either side; the remaining 
two stand on edge below, with their margins in con- 
tact, enclosing the stamens and pistil. An insect visit- 
ing the flower alights naturally on the keel or pair of 
lower petals. Pressed down by its weight, these open, 
often with a sudden movement like bursting, and dust 
the insect with pollen. Compare also the flowers of 
the Snapdragons (Antirrhinum) and Toadflaxes 
(Linaria), in which the upper and lower lips of the 
corolla meet like a closed mouth, which can be forced 
open only by a strong insect like a bee, and is safe from 
predatory visits of smaller fry (Fig. 18). In the Sages 
(Salvia) the corolla is tubular at the base; there is a 
large lobed lip on which visiting insects alight, and a 
hooded roof above arching over the stamens and pistil, 
which are placed close against it, overhanging the 
entrance to the corolla-tube, at the base of which the 
