PESTS OF ORCHARD AND FRUIT GARDEN. 



17 



Plum Gummosis. 

 Cladosporium epiphyllum (Link.), PI. 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. 



Keio Bulletin, 1899, p. 1, pi. ; Mass. PI. Dis. 306 ; Sacc. Syll. iv. 

 1718. 



Plum-tree Rust. 

 Puccinia pruni (Pers.), PI. XI. fig. 15. 



Nearly all kinds of Plum trees are subject to the ravages of the Plum- 

 tree rust, but those attacks are not in all cases equally virulent. One 

 tree may be seen in an orchard with hardly a leaf untouched, whilst 

 another tree at twenty yards' distance will scarcely reveal a pustule. 



The under side of the leaves are generally closely sprinkled with the 

 pustules, which split irregularly and discharge the spores, light brown or 

 rusty brown for the uredospores, dark brown for the teleutospores, in 

 both cases powdery, and soon sprinkled over the leaf. 



The uredospores are egg-shaped or Pear-shaped, and the whole sur- 

 face minutely spiny (20-35 x 12-16 fx). These are the ordinary uredo- 

 spores, or, as we might call them, the true uredospores. In order to 

 meet a difficulty certain authors have recently professed that two kinds 

 of uredospores are known, the second and last invented kind being 

 elongated and of a Uromyces type, so much so that it has acquired the 

 name of Uromyces amygdali. Whether this is also a Uredo form of 

 Puccinia pruni does not interest us much, as we intend, in this place, to 

 treat them as distinct diseases. 



The teleutospores are divided in the centre into two cells, each of 



c 



