206 DISEASES OF CULTIVATED PLANTS 



off. In early spring infected shoots are readily recognised 

 by the much injured bark or skin which is frequently torn 

 into shreds, more especially near the base of the last year's 

 shoot. At this period of the year the exposed, blackish 

 patches are densely covered with the Fusidadium form of 

 fruit, which is carried by wind, rain, etc., on to the young 

 leaves, which become infected. On the leaves the fungus 

 first appears under the form of small, roundish, dark- 

 coloured spots, mostly on the upper surface. These spots 

 soon increase in size and run into each other, forming 

 large, irregularly shaped, blackish-olive blotches, which under 

 a pocket-lens present a dendritic or fibrous appearance 

 towards the margin due to the extension of the blackish 

 mycelium in the tissues of the leaf. At first the mycelium 

 spreads in the leaf under the skin, which is eventually 

 ruptured, exposing numerous Fusidadium conidia, similar 

 to those produced on the year-old shoots. The conidia 

 formed on the leaves, also from the shoots, are in turn con- 

 veyed to the young fruit, which becomes infected, and the 

 result is apple scab. On the fruit the fungus forms the well- 

 known, irregularly shaped, slightly sunken blackish patches 

 or scabs, which under the pocket-lens presents the same 

 dendritic or radiating appearance, as seen in the spots on 

 the leaves. Some kinds of apple show gaping cracks when 

 scabbed ; this is because the outer portion of the fruit be- 

 comes rigid and unyielding under the influence of the 

 fungus and ceases growing, hence the internal pressure 

 causes the outer rigid portion to crack. 



Ascigerous form. Perithecia globose with a short neck, 

 90-160 //, diam., with or without bristles above; asci 8-spored, 

 40-70 /x long; spores yellowish-green, unequally 2-celled, 

 upper cell shorter and broader than lower, 1 1-15 x 4-8. 



Conidial form. Effused, velvety, olive, forming dendritic 

 patches, mycelium consisting of a compact mass of erect, 

 closely septate brown hyphae ; conidiophores closely septate, 

 brown, 50-60X4-6, outline wavy or nodulose, conidia 

 solitary, terminal, obclavate, yellowish-olive, for a long 

 time continuous then i-septate 30 X 7-9 p. 



Alderhold states that V. inequalis occurs not only on 

 the apple (Pyrus malus] but also on allied species of Pyrus, 

 excepting P. communis. A variety occurs on Sorbus, 

 and probably on species of Crataegus. From the above 

 account it will be seen that the young apples are mostly 



