Fungi 199 



If the material gets through the first four stages without shrinking 

 but collapses at the fifth, put it into 10 per cent glycerin and allow 

 it to thicken as usual. In either case, after washing in water it is 

 better to follow the Venetian turpentine method. 



All the later perithecial stages are easily cut in paraffin. 



Penicillium. -This green mold is found everywhere upon de- 

 caying fruit, upon bread, and upon almost any decaying organic 

 substance. Material is even more easily secured than in case of 

 Aspergillus, and Penicillium is an easier type for laboratory study. 

 Such a satisfactory study can be made from the living material that 

 it is hardly worth while to fix and stain. The very rapid method 

 described for Aspergillus will furnish good mounts if permanent 

 preparations are desired. 



The Erysipheae. -The mildews are found throughout the summer 

 and autumn on the leaves of various plants. Some of the most 

 abundant forms are Microsphaera alni on the common lilac ; Sphaero- 

 theca castagnei on Bidens frondosa and other species, on Erechtites 

 hieracifolia, and on Taraxacum officinale; Uncinula necator on 

 Ampelopsis quinquefolia, and U. salicis on Salix and Populus; 

 Erysiphe commune on Polygonum aviculare; and Erysiphe cichoria- 

 cearum on numerous Compositae and Verbenaceae. For herbarium 

 purposes they may be preserved by simply drying the leaves under 

 light pressure. When needed for examination the leaf should be 

 soaked in water for a few minutes, after which the perithecia may 

 be scraped off and mounted in water. In mounting great care must 

 be taken not to break off the appendages. The asci may be forced 

 out by pressing smartly on the cover (Fig. 54). 



For permanent mounts of entire perithecia with appendages, fix 

 in 5 per cent formalin 24 hours, wash in water 1 hour, stain in aqueous 

 eosin 24 hours, treat with 1 per cent acetic acid 1 minute, wash thor- 

 oughly in water, and then transfer to 10 per cent glycerin and follow 

 the Venetian turpentine method. If chromic acid, corrosive subli- 

 mate, or alcohol be used for fixing, the appendages become brittle and 

 very easily break off. However, the chromo-acetic mixtures are 

 better if it is desired to make paraffin sections showing the develop- 

 ing of the perithecium with its asci and spores. For this purpose 



