solution of isinglass in spirits of wine, which, when liquefied in a vessel plunged in water of the temperature of 25°-30°C., is greedily imbibed by the earth, and becomes inspissated into a solid gelatine at a temperature below 15°. This solution may be applied until the earth becomes thoroughly saturated, and after it is perfectly dry, the specimens will possess sufficient hardness and tenacity, and may then be mounted like the others. So far, however, as my own experience goes, I have found a weak solution of gum-arabic, frequently repeated, and applied to the under surface and edges of the specimens, to be quite as efficacious; and if after becoming thoroughly dry, they be first affixed by a thicker solution to slips of thin tissue-paper, they will be equally ready for being mounted as above. Either of these two methods may also with advantage be applied to such species as grow upon decayed mosses. Slight pressure may be applied to the thallus of fruticulose, filamentose, and foliaceous species, in order that they may lie better in the herbarium; but this should be done only to a very limited degree, so as not to obliterate the normal appearance of the branches or lobes. As the character of the under surface of the thallus is frequently of great importance, at least in foliaceous and fruticulose plants, a portion of this, not necessarily detached, should be turned over, for facility of inspection, and pressed down on the paper, before the specimens have become quite dry and rigid. In order to destroy any insects that may be upon the plants when gathered, or by which they may afterwards be infested, lichenists at one time were in the habit of poisoning them with corrosive sublimate. Frequent exposure, however, to the air in dry weather, and the presence of a little camphor, will be quite sufficient to prevent any mischief from this source. [Illustration: Fig. 43. Section of _Physcia parietina_. _a._ Paraphyses. _b._ Asci with spores. _c._ Hypothecium. _d._ Section of apothecium. _e._ Spore.]