By examination of a leaf we notice its form, the condition of its margin, whether entire or serrated or bordered; the presence and extent of the nerve; and lastly, and most important of all, the form and condition of its component cells; and for this a higher power is required. With a 2/3-inch object-glass and C eyepiece we can observe their form, and whether their walls are thickened so as to render them dot-like; their contents, whether chlorophyllose or hyaline; and their surface, whether smooth or covered with papillæ; for often these points are so characteristic, that by them alone we can at once refer a barren specimen to its proper family or genus. _Preservation of Specimens._--This may be discussed under two heads: 1st, as microscopic objects; 2nd, for the herbarium. 1. The parts required for microscopic examination are the capsules and peristome, entire specimens of the smaller species, and detached leaves. The capsules having to be viewed by condensed light, must be mounted dry as opaque objects; and for this purpose I use Piper's wooden slides, with revolving bone cover; and in one of these we may fix a capsule with the lid still attached, another laid on its side, but showing the peristome, and a third with the mouth of the capsule looking upward, a position very useful for the species of _Orthotrichum_, as we are thus enabled to see the inner peristome; and with them also may be placed the calyptra: should the cost of these be an object, a cheaper substitute may be found in shallow pill-boxes, blackened on the inside. To preserve the leaves in an expanded state we may employ the fluid media used for vegetable tissues, or, when time is of consequence, Rimmington's glycerine jelly is a convenient material in which to mount them, a ring of dammar cement being first placed on the slide, and within this the liquefied jelly, to which the expanded specimen is quickly transferred, and the cover securely sealed by gold size. Preparations of this kind are of the highest value as types for comparison with actual specimens we may have for determination. [Illustration: Fig. 37. _Ceratodon purpureus._ _a._ Male plant. 1. Leaf and its areolation. 2. Capsule. 3. Calyptra 4. Two teeth of the peristome.]