260 METHODS IN PLANT HISTOLOGY 



safranin, gentian violet, orange. The centrosomes show up well and 

 the radiations should have a clear, sharp violet color against an orange 

 background. Sections should not be more than 5 n thick; 2 /x and even 

 1 n sections are worth while, if well cut. Reniember that a ribbon which 

 doubles in length when warmed in water is not well cut. When sec- 

 tions lengthen more than 20 per cent, either cut thicker or cool, with 

 ice if necessary, until the stretching of the ribbon is down to 20 per 

 cent or less. With a room temperature of — 2° C, 52° Grubler paraffin, 

 a Spencer Student's Sliding Microtome, and a specially hardened 

 Watts safety razor blade, a ribbon of Peziza should be cut so smoothly 

 at 1 /x that it will not stretch more than 15 per cent; at 5 At, there 

 should not be more than 10 per cent of stretching when the ribbon 

 is floated on water and warmed; at 10 fi, there should be practically 

 no stretching. 



Iron-alum haematoxylin is better for the centrosomes and for the 

 young "hook" stages in the formation of the ascus, but not so good for 

 the radiations. 



Morchella esculenta is very good for the development of the ascus 

 because the nuclei are very large. 



For showing the ascogonium, ascogenous hyphae, and the origin of 

 the asci, nothing is better than Pyronema. Fix in formalin acetic acid 

 (10 c.c. formalin, 5 c.c. acetic acid, and 85 c.c. water) for 24 hours or 

 more; wash in water and stain in eosin. Or, fix in the Chicago chromo- 

 acetic-osmic solution and stain in iron-alum haematoxylin. In either 

 case, use the Venetian turpentine method and tease the material so as 

 to obtain instructive views. 



Eurotium. — Eurotium with its conidial stage, Aspergillus, is a very 

 common mold found on bread, cheese, decayed and preserved fruit, 

 etc. In the conidial stage it is green and in the ascosporic stage, yel- 

 low, reddish yellow, or reddish brown. Aspergillus is almost sure to 

 appear upon bread which is kept moderately moist, because the 

 conidia are usually abundant in the atmosphere. If the bread be wet 

 with a 10 per cent solution of cane-sugar or with grape juice, this stage 

 appears sooner and in greater abundance. A temperature of 22° to 30° 

 C. is also a favorable condition. 



The perithecial stage is not found so frequently, but can sometimes 

 be secured by examining moldy preserves. The sexual stage has been 

 induced. Soak a piece of bread in a 20 per cent solution of grape-sugar 

 in grape juice; upon this sow the spores and keep at a temperature of 



