APHIS VASTATOR. 71 



the same period, and then a vast cloud of them is formed, 

 which flies to some new locality, there to renew its ravages. 

 This cloud appears in the distance in the form of a mist. 

 I have seen the whole air filled with the flying insects. I 

 have even observed the creatures to settle upon myself in 

 the streets in the centre of London ; and, in fact, wherever 

 I have been, there have I seen the destroyer winging its 

 way to commit further destruction. 



(283.) When the plant is freed from its pest it will some- 

 times grow, and send forth new roots to nourish the stem, 

 and the haulm will thus retain much of its vigor. If, how- 

 ever, the plant has been once seriously damaged, it will 

 perish without a second attack of the Aphides, upon the 

 principle which I have heretofore pointed out, namely, that 

 a diseased potatoe will grow a diseased plant. 



(284.) When the vastator attacks the potatoe, each leaf 

 is separately destroyed, and the mischief may extend to the 

 stalk and root. In many cases the progress of the disease 

 is at first from above downwards. 



(285.) The effect of the destroyer may be watched upon 

 a sprig of potatoe placed in water : we then see very clearly 

 the mode in which the leaf dies and withers up. The vas- 

 tator passes over a field like a blast ; it damages the root, 

 lessens the vital power of the plant, and the insect then as- 

 sumes the winged state and flies away. 



(286.) This vastator does not commit the same amount 

 of mischief upon every kind of potatoe. It dislikes those 

 leaves where moisture is to be found on the under surface 

 in the morning ; and thus, according to the state of the 

 plant, it passes over with greater or less rapidity. 



(287.) The wild potatoe at Chelsea appears especially 

 to resist its deleterious action, for although I found thou- 



