6 BLIGHTS, ORCHIDS AND PERNS 



completely destroyed by a blight. The ordinary observer might not 

 easily distinguish between blights and mildews {Peronospkorea) , but 

 the treatment is easier in the former, which do not penetrate the 

 tissues of the host. In instances where the damage seems considerable, 

 it would be best to send a sample to some one familiar with these 

 minute forms for determination, and probably he will be able to give 

 such remedies as are found in the bulletins of the agricultural stations. 



All the fine print following consists of the descriptions of Dr. T. J. 

 Burrill, which are used by permission, in order that this work may be 

 used in our classes. The descriptions of the Illinois bulletin were fol- 

 lowed to the extent of omitting "sometimes colorless" in describing the 

 appendages of .5'. Castagnei and a term meaning the same in describ- 

 ing those of E. Cichoracearum, Also the term "inconspicuous'' was 

 allowed to remain in describing the mycelium of U. circinata as found 

 in the bulletin. Otherwise, the descriptions are those found in 

 Pyrenomycetes of North America. In the three instances, the de- 

 scriptions in the bulletin suited our specimens better. 



Key to the Genera of Erysiphe^E. 

 Appendages consisting of simple threads similar to the mycel- 

 ium, and often interwoven with it. A. 

 Appendages dissimilar to, and free from mycelium. .B. 



A. Perithecia containing only one ascus. . Sph^Erotheca. 

 Perithecia containing several asci. . Erysiphe. 



B. Appendages simple, not usually forked at the tip. . I. 

 Appendages dichotomously forked at the tip. .2. 



t. Appendages coiled at the tip, asci several. . Uncinula. 



Appendages needle-shaped, abruptly swollen at base, 

 asci, several . . Phyel actinia. 

 2. Perithecia containing only one ascus. Podosph^Era. 



Perithecia containing several asci. . Microsph^Era. 



Sphaerotheca, Lev 



Perithecium containing only one ascus. Appendages simple threads not unlike 

 the mycelium with which they are frequently interwoven. Ascus suborbicular, 

 usually containing eight sporidia. Very rarely two asci have been observed. 



i. vS. pannosa, (Wallr.) Lev. 



Mycelium abundant on the leaves, stems, etc., often sterile; perithecia more 

 often occurring on the branches, scattered, delicate, 90-100*//, reticulations evident, 

 small, 10 -15 //; appendages short and delicate, much interwoven with the mycelium, 

 sometimes colored; ascus large, delicate, ovate, expanding, when free from the 

 perithecium, to a length greater than its diameter; sporidia 8, large, 29// long. 



* Italic // is used for micro-millimeter instead of the Greek character. 



On Rosa blanda. 



In my specimens, the appendages were frequently as long as those 

 of S. ( 'astagnei, but they were not so flexuous; and the reticulations of the 

 perithecia were much smaller. 



2. vS. MORS-UV.fi. (vSchw. ) B. & C. 



M jrcelium abundant, at first white, becoming dark brown, densely covering the 

 leaves, stems and fruit; perithecia most abundant on the stems and "fruit, densely 

 aggregated, embedded in the thick felted mycelium, variable in size. 00-120 //. daric 



