beautiful when viewed with a tolerably high power. The number of foreign ferns now cultivated in this country has greatly widened the field for research in this direction; and it may also be mentioned that the under-sides of many are found to be covered with “scales” of very beautiful forms. A small piece of the frond of one of these may be mounted in its natural state, but the removal of the “scales” for examination by polarized light will be described in another place. The mosses also are quite a little world, requiring but a low power to show their beauties. The leaves are of various forms, some of which resemble beautiful net-work; the “urns” or reservoirs for the spores, however, are perhaps the most interesting parts of these objects, as also of the “liverworts” which are closely allied to the mosses. These “urns” are generally covered by lids, which fall off when the fruit is ripe. At this period they are well fitted for the microscope. The common screw-moss may be found in great abundance, and shows this denudation of the spores very perfectly. Many of these may be easily dried without much injury, but they should also be examined in their natural state. The student should not omit from his cabinet a leaf of the nettle and the allied foreign species, the mystery of which the microscope will make plain. The hairs or stings may also be removed, and viewed with a higher power than when on the leaf, being so transparent as to require no balsam or other preservative. There are few more interesting objects than the _raphides_ or _plant-crystals_. These are far from being rare, but in some plants they are very minute, and consequently require care in the mounting, as well as a high magnifying power to render them visible; in others they are so large that about twenty-five of them placed point to point would reach one inch. Some of these crystals are long and comparatively very thin, which suggested the name (_raphis_, a needle); others are star-like, with long and slender rays; while others again are of a somewhat similar form, each ray being solid and short. If the stem of rhubarb, or almost any of the hyacinth tribe, be bruised, so that the “juice” may flow upon the slide, in all probability some of these crystals will be found in the fluid. To obtain them clean, they must be freed from all vegetable matter by maceration. After this they must be thoroughly washed and mounted “dry.” They are also good _polarizing_ objects, giving brilliant colours; but when used for this purpose they must be mounted as described in Chapter III. A few plants which contain them may be mentioned here. The Cactaceæ are very prolific; the orchids, geraniums, tulips, and the outer coating of the onion, furnish the more unusual forms.