30 MICROSCOPIC OBJECTS. 



will be found examples of the most curious kinds. They 

 require a shallow magnifying power; from 30 to 70 

 diameters being generally sufficient. 



Aphis Vastator. — This insect (the larva of which is 

 supposed by some naturalists to be the cause of the 

 disease in the potato) has of late attracted much atten- 

 tion. As a microscopic object it does not possess any 

 remarkable features, except indeed the two air-tubuli 

 near the posterior extremity of the body. 



The interest and importance which attach to the potato, 

 and the prevalence of disease to which it has lately been 

 subjected, and through which a large portion of our popu- 

 lation have been deprived of a valuable article of food, 

 render it desirable that a few remarks should here be 

 offered on this matter. 



The subject of the diseased state of the potato has 

 been deemed worthy the attention of the Government, 

 who caused an investigation to be made into its nature 

 and causes by eminently scientific men ; besides which, 

 many of our first botanists and microscopic observers 

 have devoted all their talents and energies to the detec- 

 tion of the cause of the evil and to the discovery of 

 means adapted for the prevention of its recurrence. 



The writer of this is induced to believe that nearly all 

 the examinations of these savans have been directed to 

 the effects, rather than the cause of the disease in 

 question. The result of this mistake has been that 

 nearly all the recommendations of scientific men have 

 proved wholly unavailing and useless. 



