FUNGOID PESTS OF CULTIVATED PLANTS. 177 



CORIACEOUS-LEAVED SHRUBS, 

 or Evergreens, are represented by the following. 



RHODODENDRON GALLS. 

 Exobasidium Rhododendri (Cram.), PI. XVI. fig. 1. 



The gall-like swellings on the leaves of Rhododendron ferrugineum- 

 and R. hirsutum, and possibly of other species, are sufficiently striking 

 not to escape the notice of even a casual observer. They vary in size 

 from that of a pea to that of a marble, and are often found several of 

 them together in a cluster. At first they are of a pale yellowish-green 

 colour, then they acquire a reddish or roseate tint, especially on the sunny 

 side. When fully and properly mature, the surface is covered with a, 

 delicate frosty bloom, like the bloom on a plum. It is in this "bloom " 

 that the fungus exhibits itself, for the mycelium is concealed within the 

 tissues of the gall. 



The fruiting consists in the development of erect stout spore-bearers, 

 called basidia, which resemble the same organs on the gills of an Agaric. 

 The apices of these basidia carry a definite number, usually four, 

 apicules, each of which supports a spore, or basidiospore. These spores 

 are colourless, elliptical (8-10 x 6-7 /-), and readily fall away. These galls 

 differ essentially from the Peach blister in the spores being naked and 

 exposed, not enclosed in asci, and in being produced upon the outer 

 and convex, not on the inner and concave surface. 



Known also in France and Germany. 



Diseased leaves should be burnt as soon as the fungus shows itself, 

 and before spores are produced. 



Sacc. Syll. Hym. ii. 7797 ; Gard. Chron. 1879, p. 119, 182; Mass. 

 PL Dis. 168, 398, fig. 



Similar galls are produced on Bay-Laurel. 



RHODODENDRON LEAF- SPOTS. 



Several kinds of leaf-spot are known on species of Rhododendron, but 

 have never caused anxiety, as they simply disfigure the leaves. Some of 

 these may be enumerated. 



Phyllosticta Saccardoi, forming orbicular spots with a tawny margin, 

 and small sporules (4 x 1 //), in France and Portugal. 



Phyllosticta rhododendricola, with large irregular grey spots having 

 a brown margin, and larger sporules (8-10 x 8 /i), in France. 



Phyllosticta Rhododendri, with rusty-brown spots, chiefly marginal, 

 and the sporules oozing out in flesh-coloured tendrils. Found in Belgium 

 and Britain. 



Phyllosticta maxima, with large brown spots with dark margin, and 

 rather large sporules (10-12 x6-8/*), confined to North America ; with 



Septoria Rhododendri, having orbicular pallid spots girt by a dark 

 purple margin, and thread-like sporules (40 p. long), and a similar 



Septoria solitaria, with sporidia half as long, on Rhododendron occi- 

 dentale in California. 



