Sphaerotheca CT 



[W. Indies. — Jamaica {76).'] 



[South America. — Quito, Ecuador (275).] 



The present species is sharply marked off from all the species 

 of the Eiysiphaccac by its pannose satiny patches of persistent 

 mycelium, in which the perithecia are usually completely immersed. 

 Under the microscope these patches are seen to be composed of 

 special hyphal branches from the ordinary .vegetative mycelium, 

 about 6 IX wide, somewhat rigid, more or less straight, sparingly 

 branched, with numerous free, somewhat tapering ends. The 

 hyphae are thick-walled, becoming more or less solid at maturity 

 through the obliteration of the lumen, and are shining white and 



refractive, so that each hypha has somewhat the appearance of a 

 solid glass rod. Among these densely interwoven hyphae the 

 perithecia are produced. These are interesting in being some- 

 times distinctly pear-shaped ; the appendages are short, or quite 



rudimentary. 



Although 5. pannosa in its Oidium-stdig& {0. lencoconium 

 Desmaz.) often covers the upper surface of rose-leaves. I have not 

 been able to find, in the considerable amount of material exam- 

 ined, any perithecia formed here. It is only rarely, indeed, that 

 perithecia are formed on the leaves at all (the stem usually being 

 chosen), and then it is always In the characteristic pannose patches 

 on the petiole or at the back of the midrib, and not scattered over 



the surface. 



It has frequently been asserted that the mj-cellum of 5. pan- 

 nosa is perennial, and reappears in successive years on the same 

 shoots of infected roses, and it has been supposed by many authors 

 that the mycelium is capable of entering at times into the tissues 

 of the host-plant, although no direct evidence exists, apparently, 

 to support this view \cf. Winter (394, P- 26) and Schroeter (319, 

 p. 230) where the author remarks : Dieser Pilz kann auf den 

 befallenen St5cken uberwintern und wird selbst durch Pfropfreiser 

 ubertragen "). In the examination of shoots of rose-bushes cov- 

 ered with patches of 5. pannosa in different stages of development, 

 I have found only the usual haustoria In the epidermal cells, and 

 no signs of an internal mycelium. It was noticeable, too, m the 

 specimens examined that the fresh centers of disease which ap- 

 peared in the spring did not occur at the places (marked by con- 



