248 VEGETABLE FOES AND DISEASES 



aperture by which beetle has come out ; m, cavity soaked 

 with paraffin oil and made offensive to Snake Millipedes and 

 other pests ; n, radicle ; o, ascending axis or plumule. H, 

 germination of Broad Bean that was infested with Bean 

 Beetle when sown and seed not dressed : />, cavity formed by 

 Beetle in Bean and ascending axis or plumule destroyed ; ^, 

 radicle quite normal, but the grower is disappointed because 

 no growth appears above ground and the seed lobes are gener- 

 ally infested by millipedes and rapidly decay. I, infested 

 Broad Beans after treatment with paraffin oil and remaining 

 overnight : r, small holes by which beetles have passed out of 

 Beans ; s y dead beetles. 



THE POTATO DISEASE (Phytophthora infestans). 



This destructive pest was first observed in the 

 United States, Denmark and Norway between 1840- 

 42, and by 1845 ^ nac ^ spread over Europe, doing 

 immense damage, especially in Ireland. In the first 

 ten years of its invasion the injury was very severe, 

 and though less malignant at the present day, it is still 

 the cause of much damage, particularly in wet seasons. 

 It not only attacks the Potato and Tomato, but infests 

 several exotic and native species of Solanum. 



History. The disease is first indicated by brownish 

 blotches on the leaves. These, small at first, gradually 

 increase in size and cause the leaves to curl, followed 

 by a blackening and decaying of the leaves and stems, 

 the affected crop collapsing in a few days and emitting 

 a disagreeable smell in cases of severe infection. With 

 a pocket lens numbers of delicate white threads are seen 

 towards the circumference of the diseased and brown 



