FERTILIZATION. 173 
ing essential organs of two forms, Fig. 157. Such flowers 
are said to be dimorphous (of-two-forms). In the short-styled 
flowers, I, II, the anthers are borne at the top of the corolla 
tube a, S, and the stigma, g, stands about half-way up the 
tube. In the long-styled flowers, III, IV, the stigma G is at 
the top of the tube and the anthers, S, are borne about half- 
way up. An insect, pressing its head into the throat of the 
corolla of I or II would become dusted with pollen which 
would be brushed off on the stigma of a flower like III or IV. 
On leaving a long-styled flower, IV, the bee’s tongue would 
be dusted over with pollen, some of which would necessarily 
be rubbed off on the stigma of the next short-styled flower 
that was visited. Cross-fertilization is insured, since all the 
flowers on a plant are of one kind, either long-styled or short- 
styled, and since the pollen is of two sorts, each kind sterile 
on the stigma of any flower of similar form to that from 
which it came. 
Trimorphous flowers, with long, medium, and short styles, 
are found in a species of loosestrife.? 
211. Studies in Insect Fertilization. —The student cannot gather 
more than a very imperfect knowledge of the details of cross-fertilization 
in flowers without actually watching some of them as they grow, and 
observing their insect-visitors. If the latter are caught and dropped into 
a wide-mouthed stoppered bottle containing a bit of cotton saturated 
with chloroform, they will be painlessly killed and most of them may be 
identified by any one who is familiar with our common insects. The 
insects may be observed and classified in a general way into butterflies, 
moths, bees, flies, wasps, and beetles, without being captured or 
molested. 
Whether these out-of-door studies are made or not, several flowers 
should be carefully examined and described as regards their arrange- 
ments for attracting and utilizing insect-visitors (or birds). The following 
list includes a considerable number of the most accessible flowers of 
spring and early summer, about which it is easy to get information from 
books. 
1 See Miss Newell’s Reader in Botany, Part I1, pp. 60-63. 
