28o PLANT DISEASES 



The young shoots, leaves, and fruit are attacked, the 

 disease often appearing in the spring and continuing till 

 the cessation of active growth of the host. On the leaves 

 the fungus forms small, irregularly scattered, greyish spots, 

 bordered by a dark line ; sometimes the central portion of 

 the spots becomes dry, brittle, and eventually falls out, form- 

 ing holes in the leaf. On the young shoots, tendrils, and 

 leaf-stalks the spots at first resemble those on the leaves, 

 but soon become elongated ; the central portion sinks 

 owing to the decay of the tissues, the bark and under- 

 lying wood, sometimes down to the pith, being destroyed 

 by the fungus. The spots on the fruit usually retain a 

 circular outline and become larger than those on the 

 leaves, and not unfrequently run into each other, forming 

 irregular blotches, and have a bright red ring inside the 

 blackish border, hence the American name, ' Bird's-eye rot.' 



The growth of diseased fruit is arrested, and finally it 

 shrinks and dries up, still remaining hanging. As a rule 

 all the grapes in a cluster become diseased, one infecting 

 another. The grey central portion of the patch becomes 

 studded with black points when mature, which when 

 examined under the microscope are seen to consist of 

 dense tufts of upright, slender branches or conidiophores, 

 each bearing a minute, colourless conidium at its tip. 



These conidia germinate quickly in water, and are 

 washed by rain and dew, or carried by insects or birds 

 from one tree to another, and thus spread the disease. 



Preventive Means. — This disease is undoubtedly very 

 difficult to combat successfully. Dredging with flowers of 

 sulphur may be practised on the shoots and leaves, repeat- 

 ing at intervals of ten days if the disease continues to 

 spread. A small quantity of quicklime should be mixed 



