Sphaerotheca 69 



in Europe, with its distinct habit, the remark of Burrill (60, p. 6), 

 that the afifinity bet\veen 5. pannosa and 5. liinnuli is quite as 

 close as between S, liniiiuU and its variety fidiginca appears 

 strange, and still more so does Earle's note on the specimei^ of 

 *' 5. pannosa " in Seymour and Earless Economic Fungi, no. i 3 Ta, 

 that *' this form Is so like 5. huniuli (DC.) Burrill that it causes 

 doubt in my mind as to whether the two can be kept distinct.'* 

 On examining American material it became at once clear that 

 what has passed in the United States for 5". pannosa is for the most 

 part a quite distinct species, viz, 5. lunmdi. This form of 5. 

 Jiiunuli on rose-leav^es is a ver}^ interesting one, and when, as is 

 frequently the case, the appendages are colorless and shining, 

 is identical with "5. pniinosa'' on Rhus, At other times 

 however, the appendages are more or less colored, and there seems 

 little doubt that Earle's opinion that the form is not distinct from 



5. huniuli is correct. 



It is a most interestincf fact that in America 5. Junnuli should 



have attacked roses, while in Europe, where 5. luimnli is equally 

 common, only 5. pannosa is known on this host. The case, how- 

 ever, is quite analogous with that of another species of the Ejy- 

 siphaceae, viz, Microsphacra alni which is very common in the 

 United States on Syringa vulgaris, yet in Europe, where both the 

 fungus and the host-plant occur frequently, there is no record of 

 the lilac being attacked by M. alni, 



I have seen only two specimens of true J?, pannosa from America 

 •one in Seymour and Earle's Economic Fungi, no. 131b, on 

 ^^^^sp. from Tennessee ; the other sent to me by Professor G. P. 

 Clinton '' on Rosa sp. ; stems ; Illinois." Owing to the confusion 

 that has existed between S. huniuli and S. pannosa, mentioned 

 above, it is impossible at present to give the distribution of the 



latter species in America. 



S. pannosa is the '* rose-mildew," so well known to rose-grow- 

 ers, and if unchecked is a dangerous disease, quickly spreadin 

 from bush to bush in its conidial {Oidinm) stage. As in the case 

 of the vine-mildew, however, a fungicide which is usually effica- 

 cious is found in flowers of sulphur, or potassium sulphide (half 

 an ounce of sulphide of potassium dissolved in a gallon of water). 

 For roses grown under glass, Maynard (243) reports that a sure 



(T 

 £3 



