FUNGI 



263 



the Venetian turpentine method. If chromic acid, corrosive sublimate, 

 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 developing of the 

 perithecium with its asci and spores. For this purpose the omnipres- 



FiG. QQ.^Microsphaera alni, the Lilac Mildew, on Syringa vulgaris. Single perithecium crushed 

 a little, so that the asci, each with 8 ascospores, are coming out. The appendages are beautifully 

 branched at the tip. Stained in eosin, which stains the appendages. X300. From Chamberlain's 

 Elements of Plant Science (McGraw-Hill Book Co., New York). 



ent Eujsiphe commune on Polygonum aviculare is exceptionally favor- 

 able, because, after the material has been fixed and has been brought 

 into alcohol, the whole mycelium, with the developing perithecia, may 

 be stripped from the leaf without the slightest difficulty, thus avoiding 

 the necessity of cutting the leaf in order to get the fungus. Material 

 in which the perithecia are still white or yellowish contain stages up to 

 the formation of the uninucleate ascus; brownish perithecia show the 



