72 APHIS VASTATOR. 



sands upon the large leaves, yet they did not destroy it to 

 half the extent that they would have done if they had at- 

 tacked some of the more highly" cultivated varieties of pota- 

 toe, and I am informed that all the tubers up to November 

 3d were quite sound. 



(288.) When the insect has damaged the leaf of the 

 plant, it is much influenced by wet weather : a shower of 

 rain will fill the stems with water : and in consequence of 

 the solid portion having been taken away by the insect, 

 the moisture cannot cause the rapid growth of the plant 

 which should take place under such circumstances. 



(289.) The sap being thus in too fluid a condition, acts 

 prejudicially, and the plant rots at the collar, the under- 

 ground stems, various parts of the upper stem, the leaves, 

 the fruit. After this disorganization all the effects which 

 I have described when treating of the disease take place. 



(290.) The amount of injury committed by the destroyer 

 is in a great measure proportionate to the period of the 

 growth of the plant at which it attacks it. If it attack it in 

 the early part. of the year, the plant is killed before the 

 tuber is formed, and the worst damage is done ; if at a 

 later period, the starch is diminished in quantity; and if it 

 attack the plant after the tubers are completely developed, 

 then the creature can do but little injury. 



(291.) It is from this cause we find that in the districts 

 where the plant was affected in July, it did so much more 

 damage than when it commenced its ravages in August. 



(292.) The first appearance of the disease in a healthy 

 and previously undamaged plant is always subsequent to 

 the visit of the destroyer ; and the amount of the disease, 

 ccRteris paribus, is directly proportionate to the number of 

 insects which take away the vital fluid of the plant. 



