Sphaerotheca 75 



'* Very conspicuous upon the growing shoots of Qucrcus agri- 

 folia — the Oidiuin as a white mealy stratum from Feb.-^Iay, fol- 

 lowed by the ascophore on the leaves below. San Francisco*' 

 (Harkness, L c). 



S. lancstris is a very conspicuous fungus In its dense scattered 

 or confluent patches, of a dull, dark -brown color when mature, on 

 the under side of oak leaves. In general habit it approaches, 

 through its persistent brown mycelium, 5. inors-2ivat\ from which 

 it is, however, quite distinct in the more closely interwoven hyphae, 

 which are much more tortuous or even angularly bent, the sepa- 

 rating inner wall of the perithecium and the larger, usually slightly 



stalked ascus. 



The inner wall of the perithecium is formed of colorless angular 

 cells, about 15 a wide, with refractive walls, and, as the perithe- 

 cium approaches maturity, becomes completely separated from the 

 outer wall. When a nearly ripe perithecium is pressed open, the 

 ascus is forced out enveloped in the still unbroken inner wall. 

 Even wHth a perfectly ripe perithecium, when the free ascus es- 

 capes, the inner wall on gentle pressure usually follows the ascus 

 in the shape of a hollow globular body split towards the apex. 

 In this character ^. lanestris, recalls 5. pJiytoptophila (see fig. 1 24). 



Burrill (60) says, " The perithecia * * * when carefully sepa- 

 rated appear to be absolutely without appendages." Although 

 this is frequently the case, I have occasionally seen a few very 

 short, pale brown appendages at the base of the perithecium, 

 usually very much shorter than, and never exceeding, its diameter. 



Harkness (158) described the Oidium form of 5. lanestris a.s 

 follows "C. ventrkosiun ; segments swelling in the center and 

 becoming barrel-shaped, 34-38 x 20-22 /i. and filled with numer- 

 ous round or elliptic bodies, 5-6 x 2-4 a, which are freely dis- 

 charged from the ends, as the joints separate." It seems prob- 

 able that what was seen was merely the granular protoplasm 



escaping from injured conidia. 



Tracy and Galloway {^61) remark of 5. lancstris, "the dense 

 mycelium completely covers the young leaves and twigs, causing 

 the former to shrivel and cease growing before they attain one- 

 fom-th their usual size." 



