54 INTRODUCTION TO BOTANY 
which is covered with a clear, sticky fluid. When a small in- 
sect touches one of the sticky knobs, it may be held fast, and 
in that case the hairs at once begin to close over it. The insect 
soon dies and usually remains for many days, while the leaf 
pours out a juice by which the soluble parts of the insect 
are digested. The liquid containing the digested portions is 
absorbed by the leaf and contributes an important part of 
the nourishment of the plant, while the undigested fragments, 
such as legs and wing cases, remain on the surface of the 
leaf or may drop off after the hairs let go their hold on the 
captive insect. The pitcher plants have cylindrical, liquid- 
containing leaves, with inner hairs so arranged that insects 
get into the leaves very easily and get out with great diffi- 
culty, if at all. The leaves of the Venus’s-flytrap close 
so quickly that they sometimes catch insects which may 
come in contact with them. 
PROBLEMS 
1. Which are greener, leaves which are densely shaded or those 
which are exposed to the sun? What makes the difference? 
2. Will alcohol dissolve the chlorophyll more quickly from densely 
shaded or from openly exposed leaves? Why? 
3. Under what conditions could a field of corn lose water to the soil 
instead of securing water from the soil? 
4. What would be the effect upon animal life if green plants should 
manufacture no more food than they consume in their own growth? 
5. Leaves often give a strong starch reaction in the late afternoon 
and none in the early morning. Can you account for this? 
6. It was found by some students that a corn plant elongates about 
four times as much between 6 p.m. and 6 a.m. as between 6 a.m. and 
6 p.m. Can you account for this fact? 
7. Fields of grain are often more or less wilted at noon on hot 
summer days and regain their turgor at night even when no rain has 
fallen. Can you account for this fact? 
8. In trying to kill plants in the lawn or trees in the cultivated 
fields people sometimes put salt upon the roots or stumps. What is the 
botanical explanation of this practice ? 
