INSECTS. 179 



gonium, and various other plants, is so small that it 

 cannot be seen by the naked eye ; but it produces what 

 is known as " black rust," a disease that in many parts 

 of the country has made the cultivation of these plants, 

 particularly the Verbena, almost impossible. 



Viewed by a powerful microscope, this insect, mag- 

 nified 400 times, appears of the size given 

 in fig. 48 ; it moves with great rapidity, 

 and can only be examined as it stops to 

 feed. When this little pest has once got 

 a foothold, all direct remedies to dislodge 

 him seem to be powerless; the fumes of 

 tobacco, so destructive to the aphis, or of 



-T7I * Q 1 



sulphur, which is death to the spider, fall 

 harmlessly on this microscopic insect. 



There is hardly a doubt but that the fumes of sulphur 

 or tobacco would destroy it, if it had not the power cf 

 imbedding itself in the leaf. This is evidently the case, 

 as on subjecting affected plants to a severe fumigation 

 with tobacco for 30 minutes no insects could be discerned 

 on the leaves ; but after a short time they again appeared 

 on the field of the microscope, apparently unscathed. 

 Now, although we have no direct remedy against this in- 

 sect, which produces the black rust, we have, I think, a 

 preventive, by keeping the plants in that healthy condi- 

 tion which seems to be repellant to its attack. For the 

 means used to get that healthy condition, see article 

 on the culture of the Verbena, which is, with slight modi- 

 fications,, equally applicable to all other plants affected 

 by this insect. 



The microscope reveals that this particular species, 

 which is so destructive to our Verbena, Heliotrope, Petu- 

 nia, and scores of other plants cultivated in the green- 

 house or garden, is the same or closely resembles that 

 which gives the roughness to particular parts of the bark 

 of cherry, plum, and peach trees, and no doubt is to be 



