FUNGOID PESTS OF CULTIVATED PLANTS. 125 



PLUM POWDERY MILDEW. 

 Uncinula Prunastii (DC.), PI. XI. fig. 17. 



This mildew resembles externally the previous species so much that it 

 is scarcely possible to detect the difference by the naked eye. However, 

 it is more commonly found on the wild Sloe than on the cultivated Plum. 



The mycelium is thin, and spreading over the surface of the leaves, 

 giving them a frosty appearance, but never very dense. The conidia, in 

 the early stage, are of the Oidium form, and are produced in short chains. 



The receptacles are globose and minute, scattered over the mycelium, 

 and scarcely visible to the naked eye. The appendages which surround 

 the base of the receptacles are very numerous and peculiar in their 

 character, inasmuch as they are unbranched and curved at their tips in 

 a hook-like manner, and are about twice as long as the diameter of the 

 receptacle. Each receptacle contains from twelve to sixteen transparent, 

 pear-shaped sacs, or asci, each of which contains six sporidia. 



This species is found also in France, Belgium, Germany, and Italy. 



As an epiphyte, should this species threaten to give trouble, it should 

 be met with the sulphur treatment. 



Sacc. Syll. i. 23 ; Cooke M. F. 239. 



PLUM GUMMOSIS. 

 Cladosporium epiphyUuni (Link.), PL XI. fig. 18. 



Gumming, as exhibited in Prunus japonica, was made the subject of 

 investigation by Massee in 1899, and the features were so apparently 

 identical with those which takes place ordinarily in Plum and Cherry trees 

 as to indicate the possibility of the cause being the same. 



Stout branches were mostly attacked, and the disease was indicated by 

 tear-like drops of almost colourless gum oozing from the branches. The 

 drops increase in size so as to form irregular masses as large as a Walnut. 

 Soft in damp weather, but in dry' shrinking and horny, they gradually 

 change in colour from grey to black as they increase in size ; but this is 

 external, as the colour diminishes towards the centre. 



A black mould (Cladosporium epiphyllum) was traced as the cause of 

 this disease, as a wound parasite, entering through small wounds in the 

 bark, or where buds have been broken off. An olive patch of the mould 

 first appears at the wounded point, and after the conidia are dispersed the 

 drop of gum appears, and into this gum the threads of the mould extend. 

 The threads are at first colourless and slender, but as the masses increase 

 the tips of the threads nearest the circumference become olive, and broken 

 up into chains of cells, many of which produce small sclerotia or compact 

 masses of cells with thick dark brown walls. If the mass remains damp 

 at this stage myriads of very minute conidia are produced by the large 

 brown cells. If the conditions remain unchanged the conidia increase 

 rapidly by gemmation. When the mass is dissolved away to the ground 

 the conidia continue to reproduce themselves by gemmation. 



Keiv Bulletin, 1899, <p. 1, pi. ; Mass. PL Dis. 306 ; Sacc. Syll. iv. 

 1718. 



