In the September number we considered flowers and their invited guests, that is the insects useful in carrying pollen. The very things which attract useful insects to flowers are attractive also to useless insects. For example, nectar in a flower seems just as desirable to an ant as to a butterfly, but the ant is a creeping insect and would be likely to lose the pollen in passing from one plant to another. If useless insects found free access to flowers and carried off their food supplies, the useful insects would soon stop visiting them. It is of great advantage to flowers, therefore, to have some means of warding off the creeping insects. It must not be understood that all plants are equally successful in this matter, or that any plant is always successful, but there are certain things which seem to hinder or discourage the approach of creeping insects to flowers.

Perhaps ants may be taken as the best illustration of the insects whose visits are discouraged by flowers. They are very much attracted to the food supplies in the flower, especially the nectar, and are among the most intelligent of insects, often overcoming the most serious obstacles. They will be considered in this paper, therefore, as the insects which are seeking the nectar and pollen of flowers without invitation. A charming little book upon this subject has been written by Kerner, and translated into English, under the title which appears at the head of this paper. It is in this book that the chief obstacles to such unwelcome guests as ants are clearly stated.

Hairs.—One of the most common obstacles to ants is a barrier of hair. For some reason, ants dislike to cross such a barrier. Travellers in tropical countries, where ants abound, tell us that a hair rope laid around a tent is a very effective barrier against the invasion of armies of ants. Hair is very commonly found upon plants, and it may be noticed that it is apt to increase in amount and prominence towards or within the flower cluster. Sometimes the flowers themselves are hairy outside, and in the case of the trailing arbutus, whose flowers close to the ground are in special danger from creeping insects, the flowers are filled with a fluffy mass of hairs. In our illustrations, the wild columbine, the Oswego tea, the sunflower, and the ox-eye daisy are all hairy plants, and difficult for ants to climb. In the September number are illustrations of the mallow, the lady's slipper, and the New England aster, all of which are hairy and discouraging to ants.

An interesting fact in connection with the wild columbine may be noted. The nectar is deposited in the knob-like bottom of the long tubular spurs, and the entrance is so carefully guarded that only a long and slender proboscis, like that of a moth or a butterfly can reach the nectar. The bumblebees, however, have learned this fact, and bite through the tips of the spurs and steal the nectar. As a consequence, the wild columbine is said to be little visited by the proboscis-bearing insects, and its pollination is seriously interfered with.

Sticky excretions.—Some plants have the power of excreting upon their surface a sticky substance like mucilage. This mucilage may be produced by hairs, which are then called "glandular hairs," or it may appear directly on the surface of the plant. When ants or other insects try to cross such a barrier they are not merely stopped but caught. Upon "glandular" plants it is very common to see small insects stuck fast, and it is more than probable that the nourishing material of their bodies is digested and absorbed by the plant. In this way the plant not merely stops the insect, but catches and devours it.

A very common illustration of such a plant is the "catchfly," whose name suggests its power. The joints of its stem are long, and near the upper end of each joint is a band of mucilage. This series of sticky bands forms a very effective barrier to any insect trying to crawl up the stem.

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 smartweeds, 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 bumble-bee 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."

In most of the orchids there is a very complete adaptation of the flower to its insect, by which almost every insect excepting one special kind obtains nothing for its visit. The nectar is usually in the end of a long spur, and to obtain it the head of the insect must just fit between two sticky buttons to which the pollen-masses are attached. The length of the spur is nicely adjusted to the length of the proboscis of the visiting insect, but his head must also be of a certain breadth. If an insect visits the flower with a proboscis too short or too long, or a head too broad or too narrow, its visit is unavailing. The danger of such narrow specialization is apparent in the case of the orchids, for each plant is so dependent upon a special insect that the disappearance of the latter seriously endangers the continued existence of the former.

Protective closure.—It has long been noticed that certain flowers open only in the evening, the evening primrose being a conspicuous example. These flowers are adapted to the visits of the night-fliers, the moths, and about clusters of evening primroses numerous large hawk-moths may be seen after sunset. During the day the flowers are closed and safe from the visits of any insect, but by opening in the evening they are not only ready for the visits of the night-fliers, but they avoid the visits of most creeping insects, notably the ants, who are not abroad after "the dew falls."

Protection against grazing animals.—Although we are considering the ways by which creeping insects are checked in their efforts to visit flowers, it seems pertinent to mention the more universal danger which comes from grazing animals. If flowers were as attractive to grazing animals as they are to insects they would be in danger of wholesale destruction. It can be observed, however, that these animals as a rule avoid the flowers of a plant, although they may strip off its leaves. It is believed that this avoidance is due to the fact that in or about the flower cluster there are usually secreted bitter, sour, or nauseous substances, which grazing animals have learned to avoid. It should not be imagined that these substances are there for that purpose, but being there the result is that the flowers are avoided. It is unknown how generally true this is, and the effectiveness of this method of protection may have been exaggerated. Those who can observe cattle, however, are in a position to test them with the flowers of the various plants they are known to eat, and determine how far they avoid them.

In conclusion, it may be of interest to call attention to the great complexity of relations existing among plants and animals by repeating Darwin's famous illustration known as "Cats and Clover." In a certain district in England he observed that the clover was pollinated by the bumblebees, which had their nests in the fields. It followed, therefore, that the more the bumblebees, the more the clover. He also observed that the field mice preyed upon the young broods of the bumblebees, and, therefore, the more the field mice, the fewer the bumblebees and the less the clover. When cats were plenty and preyed upon the field mice it followed that the more the cats, the fewer the mice, the more the bumblebees, and the more the clover. Therefore, the crop of clover depended upon the presence of cats in the neighborhood.

John Merle Coulter.