There are many other interesting things we may learn about leaves, with the help of our microscope. The cabbage leaf is quite smooth, but if we are observant we shall have noticed that sometimes each leaf appears as though it had been powdered, it has a decided bloom. The bloom does not appear on the leaf for ornament but for a purpose. It is a waxy substance and it prevents the leaf from losing moisture too quickly in dry weather. This is very important for the plant; if the moisture taken up from the soil were lost in the air too quickly by the leaves, the plants would wither and eventually die. It is not all plants which can wear a protective covering when danger threatens, most plants have either no protection or are permanently protected. There is a large class of plants with folded or rolled leaves; heather and marram grass belong to this class. We must examine some of these leaves and we shall find that all the pores are on the inside of the leaf whether it be folded or rolled. The reason for this is that moisture also escapes through the pores and, when they are thus protected, it is not carried off too quickly by drying winds. Many plants are protected, as far as their leaves are concerned, at anyrate, by hairs. They take the place of the bloom in such plants as the cabbage. There are thousands of plants with hairy leaves and they will provide as many interesting objects for our microscope. Let us examine as many as we can for the hairy covering of each plant will be a little different to the one we examined previously. There are simple hairs, quite ordinary affairs, forked hairs, branched hairs, T-shaped, star-shaped and club-shaped hairs. If we are clever with our microscope we shall notice that, however complex each hair may be it is really nothing but one cell of the skin of the leaf which has assumed a peculiar shape. The leaves of the nettle are armed with ordinary and stinging hairs; the latter are worth examining and we shall notice that there is one great difference between all the other hairs we have examined and the stinging hairs of the nettle. The former are of one cell only, the latter of several cells. A high magnification will show that the stinging hair of the nettle is not quite so simple as it appears at first sight. There are plants whose leaves are protected by very thick skins and others whose leaves become armed with hard flinty matter, so that they resemble stones rather than leaves.