IN BRYOLOGICAL WORK. 529 



The air contained in the cork-like cells of Leucobryum glaucum, 

 and other species with inflated cells, is often very difficult to dis- 

 charge. Boiling gets rid of a certain amount, especially if the 

 leaves are left in the de-aerated water for a day or two, with re- 

 boiling at intervals. Obstinate cases require exhausting with an 

 air pump. The leaves of the Sphagnaceae are especially difficult 

 if the moss is once allowed to become thoroughly dry and the 

 cells filled with air. I make a point of mounting these as soon 

 as collected, or, at any rate, of keeping the stems saturated with 

 water until I can attend to them. Bryologists attach very great 

 importance to the basal areolation, and it is necessary that the 

 leaves should come away from the stem quite complete and un- 

 injured, but it is not at all a simple matter to detach the leaves 

 from the stems previous to mounting them. With strongly 

 decurrent leaves, such as exist in Mnium stellare and in some 

 Hypna, it is almost impossible to obtain perfect specimens, and 

 it is better to remove several of the adjacent leaves, and mount a 

 portion of the stem with the leaf in situ. Generally, the most 

 satisfactory way of removing a leaf is to take hold of the apex 

 with a fine pair of forceps, and, holding the branch with another 

 pair, very gradually to strip the leaf from the stem in a down- 

 ward direction. Mosses with filiform stems and distant leaves 

 such as Amblystegium serpens, can be studied by mounting the 

 stem with the leaves attached. The strongly falcate and circin- 

 nate leaves of Harpidioid Hypna are very unmanageable, and I 

 usually strip a considerable number of leaves from the stem, and 

 mount the lot as a " spread " slide, trusting largely to luck to 

 arrange some of them in a suitable position for examination. 

 This is obviously a reckless method, but it answers very well. 



A certain amount of section cutting is necessary to the syste- 

 matic bryologist, apart from any histological investigation. The 

 leaves of the Polytrichaceae, for instance, have the surface 

 covered with longitudinal lamellae consisting of rows of upright 

 moniliform filaments. Prof. Lindberg was the first to point 

 out that these formed a valuable aid in diagnosing the different 

 species, as the transverse number and shape of the terminal cell 

 differ in each species. The only way in which they can be satis- 

 factorily examined is by means of a transverse section. 



The section Aloidea of the Tortulaceae also has lamelliferous 

 leaves, of which sections are necessary. The quickest and 



