46 



JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



Recently specimens of galls upon this plant, agreeing exactly with 

 those described by Shirai, have reached us from two different places, one 

 on the Continent and the other a garden in Cornwall. From this it 

 would appear that the disease has obtained a footing in Europe, though it 

 has probably not yet spread far enough to prove troublesome to many 

 growers. The object of this note is to draw the attention of the 

 numerous cultivators of these Azaleas to the disease, so that steps may be 

 taken immediately upon its appearance to check its spread. 



China and Japan are the countries from which at one time con- 

 siderable numbers of these plants were introduced to this country, and at 

 present plants ready for flowering are imported in large numbers from the 

 Continent, so that there is great probability of plants already infected 

 entering the country. 



The galls are of large size, measuring up to 2*5 cm. to 3 cm. in 

 diameter (i.e., up to over 1 inch), and in all the specimens I have so far 

 seen the whole of the terminal bud of a shoot has been involved in the 

 swelling. Shirai, however, states that the fungus sometimes causes the 

 malformation of a single leaf only, or even of only a portion of a leaf, 

 in which case the gall appears as a globular swelling upon the under 

 side of the leaf. The size and form of the gall in the Cornish specimen 

 are shown in the illustration (fig. 12). The gall is at first greenish, or 

 yellowish green, and glossy, sometimes where exposed to bright light 

 becoming pink, but later, as the fungus develops, it becomes covered with 

 a delicate whitish bloom, owing to the breaking through the epidermis 

 of the fruiting threads of the fungus. The spores are produced in 

 large numbers and are borne on small outgrowths from the tips of the 

 basidia, as the spore-bearing cells are called ; each basidium bears four 

 or five spores, usually four. The increase in the size of the affected leaves 

 is no doubt due to the irritation set up by the presence of the fungus, and 

 not only is the shoot which is affected prevented from flowering or 

 elongating, but a considerable amount of tho material which should have 

 been devoted to the development of other parts of the plant is withdrawn 

 for the use of the fungus and for the growth of the gall. When the gall 

 is removed from the plant it shrivels very considerably. 



The galls produced are very similar in appearance and character to 

 those common upon Rhododendron ferrngineum and R. hirsutum in the 

 Alps and in this country, the main differences lying in the difference of 

 host and the different size of the spores produced by the fungus, which in 

 this case measure about 14*5 fi in length by 4 ^ in breadth. 



The best method of controlling the pest is to remove the galled leaves 

 or shoots upon their first appearance and destroy them by fire. If this be 

 done sufficiently early before the spores are produced, there will be little 

 danger of the disease spreading. 



Similar gall-like growths are produced upon other species of Rhodo- 

 dendron through the attacks of species of Exobasidium, e.g., E. Azaleac 

 on Rhododendron nudiflorum, E. discoideum on R. viscosum, E. hemi- 

 sphaericum on R. Mettermchii ; species of Andromeda, Lebetanthus, 

 Cassandra, Cassiope, Giseckia, Ledum, Vaccinium, Symplocos, Guy- 

 lussacia, Saxifraga, etc., are also attacked. 



