TO INTERNAL CAUSES. 43 



(165.) Every particular kind of potatoe, however, is not 

 equally prone to disease, or rather, I may say, to carry 

 its individuality or peculiarity into its diseased condition. 

 The supposed original Chelsea potatoe seems to resist the 

 action of this malady nobly, the disease only attacking it 

 from leaf to leaf, and not affecting so materially the under- 

 ground stems. 



(166.) I have carefully examined this specimen, in or- 

 der to observe how it would be attacked, and I found that 

 the large leaves were all destroyed, and that the disease 

 progressed from the large leaves to those somewhat small- 

 er, and so crept on till it progressed to the top. In conse- 

 quence of this mode of attack, the main shoot and all the 

 lateral shoots were green, healthy, and vigorous, and the 

 plant appeared to a casual observer to be quite healthy ; 

 and the large leaves, or those out of sight, being alone de- 

 stroyed up to October the 16th, the plant was still growing 

 vigorously. 



(167.) At the Horticultural Society's Garden, on my 

 first visit, Uhde's wild potatoes showed the disease only 

 on the leaflet, and on a subsequent occasion there was also 

 one other leaf curled. In both cases I removed the dis- 

 eased leaf, and found that they were inhabited by a para- 

 site, which I shall hereafter describe. 



(168.) No two kinds of potatoes show the effects of the 

 disease equally ; and it is generally supposed that that po- 

 tatoe which ripens in the early period of the year, mani- 

 fests the malady less than those which ripen later, so that 

 the early Shaws are tolerably free from it. 



(169.) On examining a field in which many varieties are 

 cultivated, every sort will be found to exhibit the malady 



