FUNGOID PESTS OF CULTIVATED PLANTS. 127 



branches in early spring before the diseased fruit appears. The fungus 

 itself consists of small cylinders, or asci, standing side by side, closely 

 packed, each cylinder containing eight small globose sporidia, which are 

 ultimately ejected at the ruptured apex (4 ,u diam.). 



The sporidia germinate readily in water by the formation of a bud, 

 which assumes the form of the parent spore. The secondary spore 

 produces a bud like the first, and so on, through several generations. 



It is recommended to remove the " pockets ' ' as soon as they are 

 formed. In the United States it is the practice to cut back the branches 

 so as to destroy all parts likely to contain mycelium. 



Sacc. Syll. viii. 3342; Mass. PL Dis. 85, fig. 12; Ward, Dis. PL 

 p. 107 ; Thum. Pom. p. 88 ; Tubeuf, Dis. p. 155, fig. 



PLUM-LEAF BLOTCH. 

 Poly stigma rubra (Pers.), PL XI. fig. 14. 



These blotches are very rare upon the leaves of the cultivated Plum, 

 but are common enough on those of the Sloe. 



The blotches are orbicular or angular, of a brick-red colour, with 

 a decisive and definite outline, thicker than the leaf, with a waxy 

 appearance, and when mature dotted over the surface with darker minute 

 dots, or points, which indicate the buried receptacles which enclose the 

 fruit. 



There are two stages to this fungus : the early one in the spring 

 (Polystigmina) contains only stylospores or conidia, borne upon slender 

 threads (30 p long). 



The autumnal fruit (Polystigma) is not matured until after a period 

 of rest, such as is obtained by the fallen leaves upon the moist ground. 

 Then the fruit consists of sporidia (10 x 6 p] which are ovate, enclosed in 

 asci, and ultimately escape when mature to reproduce the species. 



Known also in France, Belgium, Sweden, Germany, Switzerland, Italy, 

 and N. America. 



Sacc. Syll. ii. 4587 ; Mass. PL Dis. p. 135, fig. 25 ; Cooke Hdbk. No. 

 2410, fig. 383 ; Grev. Sc. Cry. Fl. t. 120 ; Tubeuf, Dis. p. 189, fig. ; 

 Hart. & Somm. Dis. Tr. p. 97. 



PLUM-TREE MILDEW. 



Podospham tridactyla (Wall.), PL XI. fig. 16. 



The earliest appearance of this disease on Plum and Cherry trees is a 

 whitish mealy, or mouldy, appearance on the living leaves, which thickens 

 until the surface appears as if dusted with flour or powdered chalk ; 

 ultimately little orange, and then black, dots show themselves scattered 

 over the mealy substratum. 



In its first stage the pest consists solely of the branched and inter- 

 woven mycelium of delicate threads, which produce short erect club- 

 shaped branches, soon divided into joints, which fall away from the apex, 

 when mature, as oval conidia of the Oidium type. 



Afterwards, when the black dots appear, it has passed into the 

 Erysiphe condition, the dots representing the globose receptacles enclosing 



