262 METHODS IN PLANT HISTOLOGY 



L One hundred per cent alcohol, 2 minutes. 



2. Eosin (aqueous), 2 minutes. 



3. One per cent acetic acid, 2-10 seconds. 



4. Mount directly in 50 per cent glycerin and seal. 



If the material gets through the first three stages without shrinking 

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

 it to thicken, following the Venetian turpentine method. 



The earlier perithecial stages are more instructive when mounted 

 whole; but later stages, even before the formation of the asci, are very 

 unsatisfactory by this method, and should be cut in paraffin. 



Penicillium. — This green mold is found everywhere upon decaying 

 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 Aspergil- 

 lus 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 abim- 

 dant forms are Microsphaera alni on the common lilac ; Sphaerotheca 

 castagnei on Bidens frondosa and other species, on Erechtites hieraci- 

 folia, and on Taraxacum officinale; Uncinula necatar on Ampelopsis 

 quinquefolia, and U. salicis on Salix and Popidus; Erysiphe commune 

 on Polygonum aviculare; and Enjsiphe cichoriacearum on numerous 

 Compositae and Verbenaceae. Podosphaera may be found on the 

 leaves of young cherry trees and apple trees, and on young shoots of 

 older trees. The infected leaves are likely to be more or less deformed. 

 Phijllactinia is sometimes abundant on leaves of Ahius incana. It is 

 also found on Celastrus, Desmodium, Typha, and on various members 

 of the Amentiferae. For herbarium purposes they may be preserved 

 by simply drying the leaves under Ught pressure. When needed for 

 examination the leaf should be soaked in water for several 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 append- 

 ages. The asci may be forced out by tapping smartly on the cover 



(Fig. 69). 



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, remembering to keep all solutions slightly acid. Use 



