202 FUNGOID PESTS OF CULTIVATED PLANTS. 



Maple Mildew. 

 Uncinula Acer is, PL XIX. fig. 6. 



The Hedge Maple is apt to have its foliage nearly covered with the 

 white mealy-looking mycelium of this pest, so that they seem to have heen 

 drenched with a thin coating of whitewash. This mycelium is creeping 

 and at first superficial, and gives origin to the conidial form, or Oidium, 

 the conidia of which, falling on the leaves, increase the mealy appearance. 

 Later on the little dot-like globose conceptacles appear on the surface, as 

 in the Pea mildew. 



In this species the conceptacles are surrounded by a series of appendages 

 which are either simple or forked, and hooked at the apex. These each 

 enclose eight asci, which contain eight sporidia. A similar species is also 

 common on Willows. This was formerly called Uncinula bicomis, but the 

 name has been changed, during the craze after priority names, and to 

 gratify the vanity of priority-hunters. 



The species is recorded for the whole of Europe and Algeria. 



Sulphur and lime is the recognised application. 



Sacc. Syll. i. 27 ; Cooke, M. F. t. xi. f. 225-228 ; Cooke, Hdbk. No. 

 1914. 



Another species, Uncinula Tulasnei, occurs in the Rhine Provinces, 

 and Uncinula circinata, an American species, on Acer leaves, in the United 

 States. 



Maple-leaf Blotch. 

 Rhytisma punctatum (W.), PL XIX. fig. 7. 



This blotch resembles in many respects that of the Sycamore leaves, 

 and occurs on the leaves of Acer campestre, Pseudo-Platanus, and spicatum. 

 There are the same kind of yellow spots, caused by the mycelium, but the 

 black scab, or crust, which appears on the surface is not one continuous 

 black blotch, but consists of a number of closely crowded small frustules. 



The early stage also prevails whilst the leaves are still attached to the 

 live, and the cells or cavities of the stroma enclose only conidia, which 

 are sausage-shaped and small (4-5 x 1 //). This condition is known as 

 Melasmi/t punctata. 



The final stage, which only succeeds the wintering of the affected 

 leaves upon the ground, in like manner produces clavate asci, which are 

 narrowed at the tip, and enclose eight needle-shaped sporidia, which are 

 blunt ;it the base, and pointed at the apex, collected in a parallel cluster 

 orbundl. (:;5-40x H-2^). 



This parasite is recorded also in France, Belgium, Germany, Sweden, 

 [taly, and North America, but is not so common as Rhytisma accrinum. 



Sacc. SyM. iii. 3391, vii. 3084 ; Mass. PI. Dis. i>. 142, 378; Cooke, 

 Hdbk. No. 22K0. 



