io8 



DISEASES OF CULTIVATED PLANTS 



the other hand, if the land is not infected, if the disease 

 appears it is in one or more isolated patches, and no effort 

 should be spared to check the spread of the disease by 

 removing the diseased plants, and spraying the surrounding 

 onions. As previously stated, an epidemic of disease depends 



FIG. 24. Peronospora Schleideni. i, a 

 conidiophore that has emerged through a 

 stoma of an onion leaf; 2, free conidia ; 

 3, oospore or resting-spore. All highly mag. 



almost entirely on weather conditions; when the disease is 

 already present a few bright, dry days will cause its almost 

 entire disappearance, the onions will again begin to grow, 

 and will be but little the worse for the check. On the other 

 hand, a continuance of damp, dull weather proves disastrous. 



