FUNGI 265 



When the stroma becomes black, many members of the Xylariaceae 

 become very hard and brittle, so that sections are likely to be unsatis- 

 factory. 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 mere- 

 ly shows that such material can be cut. 



LICHENS 



For habit study, the lichens are best kept dry in a box. When 

 wanted for use, they can be taken out and sprinkled with water, which 

 will give them a bright, fresh appearance, besides making them less 

 brittle to handle. Evernia {Letharia) vulpina, the most beautiful of 

 all the lichens, and so abundant on California conifers, makes a splen- 

 did demonstration specimen when wet in this way. 



Attractive pieces of lichens like Ramalina reticulata can be stained 

 in eosin and mounted whole. Dichonema cincinnaium, Coenogonium 

 interpositum, and similar forms in which the algal and fungal elements 

 are loosely associated, can be stained in eosin, teased a little, and 

 mounted whole, making much more effective mounts than could be 

 obtained by sectioning. 



Lichens are generally regarded as difficult forms to cut. If they are 

 dry, soak them well before fixing. Formalin (5 c.c), acetic acid (5 c.c), 

 and water (90 c.c.) fixes in 2 or 3 days, but material may be left here 

 indefinitely. 



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 al- 

 ready described on page 115, satisfactory sections should be obtained 

 from thalli and mature apothecia of Physcia, Usnea, Stida, Parmelia, 

 and Peltigera. Collema and other lichens of such gelatinous consisten- 

 cy, 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. 



