FUNGI 
221 
stumps and logs, and often apparently on the ground, but really 
growing on twigs, wood, and bark just under the surface. When 
mature it is black outside and white or light-colored within. When 
young, it is easily cut in paraffin; in some forms the ascospores are 
fully formed before the stroma becomes hard enough to occasion any 
difficulty in cutting. When the stroma becomes black, many mem¬ 
bers of the Xylariaceae become very hard and brittle, so that sections 
are likely to be unsatisfactory. For general morphological study 
it is better to break the stroma transversely and examine with the 
naked eye and with a pocket lens. The asci with their spores can be 
teased out and mounted in water. For permanent preparations, soak 
the stroma for a month in equal parts of 95 per cent alcohol and 
glycerin; then cut sections, and, after leaving them in glycerin for 
a day or two, mount in glycerin jelly. It is better not to stain the 
old stages. For illustrative purposes, select forms which can be 
cut in paraffin. The method just given merely shows that such 
material can be cut. 
LICHENS 
The lichens are usually regarded as difficult forms. In younger 
stages they occasion no trouble, but an old apothecium or a leathery 
thallus often fails to cut well. By employing the gradual processes 
already described in chapter ix, satisfactory sections should be 
obtained from thalli and mature apothecia of Physcia, Usnea, Sticta, 
Parmelia, and Peltigera. Collema and other lichens of such gelatinous 
consistency, while they cut readily, show a strong tendency to wrinkle. 
Cyanin and erythrosin is a very good stain for lichens. The 
algae stain blue and the filaments of the fungus take the red. Where 
the association of the alga and the fungus is rather loose, as in 
Dichonema, more satisfactory mounts can be made by staining in 
eosin, or haem-alum and eosin, and then teasing slightly with needles 
and mounting in glycerin. 
BASIDIOMYCETES 
This is an immense group, of which the smuts, rusts, mush¬ 
rooms, toadstools, puffballs, and bracket fungi are the most widely 
known representatives. 
The Smuts (Ustilagineae).—The smuts are abundant on wheat, 
oats, corn, and various other plants. 
