Isolation. — In some cases plants or their flowers are isolated from creeping insects by water, which forms a most efficient barrier. This has been demonstrated by housekeepers, who in the days of "safes" were accustomed to set the legs of the safe in cans of water to ward off the invasion of ants. Of course, plants standing in the water are well isolated, and usually show no further device for warding off creeping insects. There is an interesting fact connected with one of our water smart weeds, which has to do with our subject. Ordinarily it stands in shallow water, and is perfectly smooth; but when occasionally the water dries up the plant becomes hairy. That this has anything to do with the danger from creeping insects is unlikely, but the hairy covering certainly appears at a very opportune time.

The teasel was once extensively cultivated as a fuller's plant, and one or two species of it have become common as wild plants, their dense and prickly flowering spikes looking like swabs for cleaning lamp chimneys. The plant is tall and coarse, and is peculiar in that its large opposite leaves unite by their bases about the stem to form a cup. In this way a series of cups is developed on the stem, and in each cup there is water. When a creeping insect crawls over the edge of the cup he sees the stem rising from a pool of water which must be crossed. As there is a series of such pools it is very unlikely that any such insect reaches the showy cluster of flowers.

The so-called "travelers' tree" of the tropics is a teasel upon a larger scale. The enormous flower cluster is at the top of the plant, and between it and the ground is a series of very large water containing cups formed by the leaves. The popular name has been given by travelers who have been represented as reaching a cup with a spear and piercing it, thus obtaining a supply of water. The story is very doubtful, and the water, usually full of the macerating bodies of insects, is still more doubtful.

Latex. — By this term is meant the milky juice which some plants possess. When such a plant is punctured or torn the latex flows out, and as soon as it is exposed to the air it becomes more and more sticky until it hardens.

It is from the latex of certain trees that India rubber is obtained, but it may be observed in many plants, notably the milkweeds, which have received their popular name on account of it.

The milkweed may be used to illustrate how latex may be of service in warding off creeping insects. In many cases the plant is entirely smooth, and the stems of the flower cluster are even slippery. When an ant reaches these slippery surfaces it clutches for a hold and its sharp claws pierce the tender skin of the plant. Immediately a drop of latex oozes out and becomes sticky, and when the ant seeks to lift its feet there is resistance, and in the struggle the claws clutch deeper, more latex oozes out and becomes more and more sticky, until finally the insect is stuck fast. The flower clusters of certain milkweeds are often found plentifully covered with small captured insects.

Protective shapes. — Many flowers secrete their nectar so that a creeping insect cannot reach it, but the suitable insect can. Illustrations are numerous, but the following will suffice.

The wild columbine, represented in one of our illustrations, secretes its nectar at the bottom of long tubular spurs, which can be traversed by slender probosces, but are impassable to creeping insects. Spurs are developed in many flowers, notably the orchids, and they are always associated with nectar secretion and the visits of proboscis-bearing insects.

In the Pentstemon, a plant whose flowers have two lips, as in the Oswego tea in our illustration, but not so prominent, the nectar is secreted in a little pit. Across the mouth of this pit one of the stamens, modified for this purpose, is placed like a drop-bar, leaving but a thin crevice leading to the nectar pit. Through this crevice a thread-like proboscis may be thrust, but a creeping insect cannot pass.

In the snapdragon the two lips of the flower are tightly closed, the lower one decidedly projecting. Any small insect reaching this lower lip as a natural landing place finds no entrance. When the bumblebee alights upon the lower lip, however, his weight depresses it and he forces his way in, and in passing to another flower effects pollination. It is interesting to note that after this first and important visit the lips remain open and other insects pass in freely, "being invited," as some one has said, "to eat at the second table."