208 
THE LIFE OF FLOWERING PLANTS 
HOME WORK 
Examine vacant lots, waste spots, and gardens for weeds. How many 
of them are composites? 
Study flowers in vacant lots, and record the results, using the follow¬ 
ing table as a guide. 
COROLLA 
Regular 
Corolla 
Irregular 
Corolla 
Lacking 
j « 
II 
sj 
V 
£2 
Pistils only 
in a Flower 
Flower 
Perfect 
Geranium . . . 
Castor bean. . . 
Salvia. 
Nasturtium . . . 
Pansy. 
Etc. 
X 
X 
X 
X 
191. Pollination. — When insects go to a plant they gener¬ 
ally have a definite errand, namely, to get pollen or nectar from 
it. As shown by the nasturtium, or the lily, they are helped 
in this by adaptations of the flower. At the same time, the 
flower has other adaptations which cause the insect to become 
covered with pollen as it leaves the flower, and still other 
adaptations which bring it about that when the insect 
enters a flower, some of the pollen from the flower last visited 
is left on the stigma of the one which it is entering. 
Pollination is only the first step in the production of 
seed. Before we can understand the use of pollination, we 
must understand the structure of the pollen grain. 
Pollen grains present the greatest variety in size, structure, 
and markings, but all have some features in common. They 
all have a double coat or covering, the outer of which is 
thin in places. When a pollen grain is caught on a sticky 
stigma, it soon sprouts; that is, the inner coat pushes out 
through the thin places in the outer coat, producing a tube. 
