144 A Monograph of the Erysiphaceae 



Amphigenous ; mycelium usually subpersistent and effused 

 over the surface of the leaf, or forming patches, sometimes evanes- 

 cent ; perithecia gregarious or scattered, globose, depressed, very 

 variable in size, 60-105 fJt m diameter, cells 8-14 ft wide ; append- 

 ages 4-30, ^ to twice the diameter of the perithecium, colorless, 

 smooth, aseptate or rarely i -septate and brownish towards the 

 base, thin-walled above, becoming thick-walled towards the base, 

 apex 3-4 times more or less closely dichotomously branched, 

 (rarely trichotomously branched in the branching of the first and 

 second orders), tips of the ultimate branches mostly straight, 

 occasionally one here and there recurved ; asci 2-7, usually about 

 4, broadly ovate to globose, 40-56 x 34-48 fi, with or without a 

 short stalk; spores 3-6, 20-24 X I(>-I2 /i. 



Hosts 



'Ifolinni, L. flava, L. liisp 



(95), Z. iviplexa, L. Intea, Z. nigral L, Pcridynienum, L. tata- 

 rica^ L. Xylostcuni^ Syringa vulgaris (3) (227). 



Distributioi. — Europe : France, Belgium, Netherlands, Ger- 

 many, Switzerland, Italy, Austria-Hungary, Sweden, Finland, 

 Russia. 



The present plant differs from M. alni only in the usually more 

 loosely branched apex, with the tips of the ultimate branches for 

 the most part straight, with occasionally one here and there re- 

 curved. At first view, one is inclined, from analogy, to consider 

 these few recurved tips as the mature form, and to dismiss the 

 straight ones as immature. Examination of considerable material 

 shows, however, that this view cannot be taken, and that the re- 



r 



curved form is really in the present plant the exceptional one. 



I'he extreme form of the var, loniccrae with a loosely and rather 

 vaguely branched apex, with the ultimate branches more or less 

 unequal, and their tips all straight, is very different from typical 

 M. alni with its compact apex and regularly recurved tips. This is 

 the form described by most authors, who consequently place the 

 plant in the section of the genus characterized by having the tips 

 of the ultimate branches not recurved. Leveille describes this 

 form (under the name of M, Dubyi)^ and figures the apex of the 

 appendages as very unlike that of M. alni. Nevertheless, in the 

 two specimens of '' M. Ditbyi^ on Loniccra Caprifolinm and L. 

 Xylostcum^ at Kew, from this author's herbarium, some perithecia 

 may be found in which the appendages have the tips of the ulti- 

 mate branches distinctly (although only here and there) recurved. 



