122 A Monograph of the Erysiphaceae 



hybrida to be able to indicate the essential specific characters 

 (probably to be found in the shape of the mature apex of the ap- 

 pendages). Tiiese two species, therefore, are not included in the 

 key; descriptions, however, of the specimens will be found at the 

 close of the account of the eenus. 



Ke> to tlie Species of ::^icrosp1iaera* 



I. Asci 2-spored, appendages densely crowded, flaccid, about equalling the diameter 



of the perithecium. 

 Asci more than 2-spored. 



6. Mougeotii. 



2. 



2. Appendages zyi-J times the diameter of the perithecium, usually much contorted 



and angularly bent, apical branching very irregular and lax, with the branches 



very flexuous and more or less curled. 9, euphorbiae. 



Appendages long or short without the above characters. ' 3. 



3. Tips of some or all of the ultimate branches of the appendages recurved. 4. 

 Tips not recurved. ji 



4. Appendages 8-12 times the diameter of the perithecium. 10 GuarinoniL 

 Appendages less than 8 times the diameter of the perithecium. 5. 



5. Appendages long and flaccid. g 



Appendages short, not exceeding 2}i times the diameter of the perithecium, not 

 flaccid. o 



6. Apex of appendages much branched, branching ornate, more or less close, spores 



Apex less branched, more or less widely forked, or branching close and simple, 

 spores 18-23 X 9-^3 ,«. 7. 



7. Appendages usually 3>^, not exceeding 5^ times the diameter of the perithecium, 



asci 3-7, ovate-globose, 3^-48/^ long. 4. alni, var. divaricata. 



Appendages 2]i~% times the diameter of the perithecium, asci 2-16, ovate-oblong, 



45-72/. long. ^ ^^^-^ ^^^^ vacciniu 



8. Appendages more or less contorted, apical branching very lax and irregular. 



4. alniy var. htdens. 

 Appendages not contorted, apical branching closer and regular. 9. 



9. Tips of the ultimate branches of the appendages not all regularly and distinctly re- 



^ curved. 4* ^^^^-^ ^,^^ lonkerae. 



Tips all regularly and distinctly recurved. jq 



10. Axis of some of the appendages not dividing dichotomously at the apex, but bear- 

 ing sets of opposite branches (Fig. 16). 4. aini, var. caiodadopkora. 

 Appendages regularly dichotomous at apex. 4 ^/^^/^ 



diameter 



Appendages colorless 



8. Russellii^ 



12. 



* jlf. umbilici and M. ferruginea are not included in this key (see above). 



