8 A Monograph of the Erysiphaceae 



4 



nuclei in the young ascus as of sexual significance, and denies the 

 primary sexual fusion of the' nuclei of the oogonium and anther- 

 idium ; but, as Wagner (3 79"*") points out, the weight of evidence 

 is against accepting Dangeard's theor}^ 



When the perithecia are about half-grown, certain cells of 

 the outer wall, situated either apically, equatorially, or basally 

 begin to grow out into the appendages. These appendages, if 

 basal, may be floccose and more or less similar to the hyphae of 

 the mycelium, with which, as in the genus ErysipJie^ they are fre- 

 quently interwoven; usually, however, they are quite distinct^from 

 the myselium, erect or radiating, and sharply characterized in 

 shape. In PJiyllactbiia they are acicular and bulbous at the base 



r 



(figs. 170, 171); in Unciniila hooked at the apex (see Plates 



j 4 and 5), and in Podosphaera and MicrospJiacra they are variously 

 branched in a dichotomous manner (see Plates i and 2). 



It is difficult to say definitely what part the appendages play in 

 the life-history of the Erysiphaceae, although it is generally sup- 

 posed that they are concerned with the distribution of the peri- 

 thecia (see Gardner, 142), 



The perithecium of Phyllactinia, besides the acicular append- 

 ages, possesses a basal mass of special branched hyphae, which 

 certainly ser\^e in the first place to attach the perithecium to the 

 leaf, and in some cases, perhaps many, causes it subsequently to 

 adhere to foreign substances. 



The asci contained in the perithecia are colorless sacs, stalked 

 or sessile, globose to cylindrical in shape, and from one to 66 (or 

 more) in number. They contain from two (or abnormally only 

 one) to eight spores. The wall of the ascus is from 1-5 ft thick, 

 and usually becomes very thin at the apex of the ascus. No true 

 paraphyses are present, although this name has been given by 

 some authors to the isolated portions of the inner wall, often of a 

 filiform shape which sometimes occurs in the perithecia (especially 

 in Phyllactinid). 



The ascopores are colorless, continuous (/. e., non-septate), 

 granular, oval, oblong, or occasionally roundish, with obtuse ends, 

 rarely slightly curved, 15-34 (rarely reaching 50) x 8-25 ;/ in size'. 



The perithecia are truly cleistocarpous, the asci being liberated 

 by the irregular rupture of the wall. This takes place in the 



