This same habit of coating its lower leaf surfaces with hair, you notice in the speckled or swamp alder, a shrub which grows also in wet places, and therefore runs the same risk of having its leaf mouths clogged with water. So when you see only the upper surface of a leaf covered with hair, you can guess that the object of the plant is to prevent too much perspiration; but when you see only its lower side clothed in this same way, you can guess that the plant fears too little perspiration. Sometimes you find a plant with leaves which have a coating of what looks almost like dust on one or both of their surfaces. This dust we call “bloom.” We see it in apples and grapes, as well as on leaves. It is made up of a waxy material which is put forth by the plant just as it puts forth hair. This bloom the plant uses also as a help to free perspiration. By thus clothing its leaves it shields the little mouths from water clogging; and so you can be sure that the little mouths have not been filled with water, and thus prevented from doing their work. The cabbage leaf has mouths on both of its surfaces, and so both sides are covered with this protecting bloom. If you dip a cabbage leaf in water and then shake it, the drops roll off and leave it quite dry. PRICKLES AND POISON Leaves need to protect themselves from other enemies than too great heat and too much water. We found that the prickly armor of the thistle enabled it to live in pastures where the cattle had killed most of the other plants. Many animals like to eat green leaves, so we are not surprised to find that plants invent different ways of protecting themselves. One look at the leaf of the thistle is enough to persuade us that it would not be very good eating. [Illustration: Prickers] The red-berried holly, with which we decorate our churches and houses at Christmas time, is another plant with prickly leaves. Some plants cover their leaves with bristles, which the cattle dread almost as much as the stout prickles. As we read before, the mullein defends its leaves by a fuzzy coat of hair. Such an armor as this is less warlike than that of the thistle, but quite as effective. Other plants fill their leaves with juices which are either poisonous or unpleasant. It seems as if animals guessed the presence of these unfriendly juices by the plant’s smell, for they will munch the different growing things all about such a plant as this, and leave the harmful leaves severely alone. The nettles cover their leaves with stinging hairs. These stiff hairs break off when handled, burying themselves in the flesh, and sending out a burning acid that punishes severely the meddler, man or beast, as it may happen to be.