156 Botanical Microtechnique 



quick reference rather than for detailed study. The production of the 

 ascigerous stage is highly uncertain, and best studied from whole 

 mounts. 



1 he Erysiphales are of interest because many members are 

 parasites of considerable economic importance. Erysiphe graminis 

 occurs on many grasses, from which the conidial stage is easily 

 obtained in abundance. The conidia are studied best by freshening 

 detached leaves in a moist chamber and examining the surface under 

 moderate magnification, wath oblique surface illumination. Microtome 

 sections are indispensable, however. Longitudinal sections of the leaf 

 show the clusters of long, finger-like haustoria in the long epidermal 

 cells. Select leaves that are young and soft, kill in Craf III, and 

 process like any young grass leaf. Iron hematoxylin is the most 

 desirable stain, although a good triple stain is indeed beautiful. 



Other interesting or important species are Erysiphe polygoni on 

 the common weed Polygonum aviculare, E. hiimuli on the rose, 

 Podosphaera oxycanthae on cherry, Microsphaera aini on lilac, and 

 Unciniila salicis on willow. For the best slides of haustoria, collect in 

 the conidial stage. Development of the perithecia can be studied from 

 successive collection up to the stage in which the perithecia begin to 

 turn gray. Kill in Craf III if the host cells are to be preserved, or in 

 Craf I for good preservation of the young perithecium. The latter 

 lluid does not seem to serve so well for the host cells. Stain as 

 reconnnended for Erysiphe graminis. Mature perithecia are very 

 brittle and difficidt to section. Furthermore, this stage is studied to 

 best advantage from dissections and macerations of bulk material 

 preserved in one of the fluids in Chap. 10. The sectioning of the 

 decayed, brittle, overwintered host leaves is a thankless and pointless 

 task except for research. 



Members of the Pezizales are of considerable cytological interest 

 as well as economic importance. Scleroiiuia fnictigena occurs on 

 cherries and plums. The conidial stage need not be sectioned, and 

 sections of the hard sclerotia are not particularly interesting. The 

 delicate goblet-like apothecia yield excellent sections. Very early in 

 the spring look for the apothecia arising from nunnmified fruits. 

 Collect cups of various sizes and preserve each in a sej)arate \ial of 

 Bouins fluid or Craf I. Successive stages of ascospore formation will 

 be obtained in this way. Longitudinal sections through the center of 

 the cup show numerous perfectly aligned asci and ascospores. Use 

 iron hematoxylin for nuclear details, but safranin-fast green shows 

 both nuclei and trania \erv well. 



