sticky hairs that close over the insect; the Venus's flytrap of the Southern states, in which the halves of the leaves close over the prey like the jaws of a steel trap; and the various kinds of pitcher plants that collect insects and other organic matter in deep, water-filled, flask-like leaf pouches (Fig. 119).
The sundew and Venus's flytrap are sensitive to contact. Other plants are sensitive to the touch without being insectivorous. The common cultivated sensitive plant is an example. This is readily grown from seeds (sold by seedsmen) in a warm place. Related wild plants in the south are sensitive. The utility of this sensitiveness is not understood.
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Fig. 119.—The Common Pitcher Plant (Sarracenia purpurea) of the North, showing the tubular leaves and the odd, long-stalked flowers.
Parts that Simulate Leaves.—We have learned that leaves are endlessly modified to suit the conditions in which the plant is placed. The most marked modifications are in adaptation to light. On the other hand, other organs often perform the functions of leaves. Green shoots function as leaves. These shoots may look like leaves, in which case they are called cladophylla. The foliage of common asparagus is made up of fine branches: the real morphological leaves are the minute dry functionless scales at the bases of these branchlets. (What reason is there for calling them leaves?) The broad "leaves" of the florist's smilax are cladophylla: where are the leaves on this plant? In most of the cacti, the entire plant body performs the functions of leaves until the parts become cork-bound.
