CHAPTER n. 

 THE DISEASES OF LEGUMINOUS CROPS. 



(1) The Parasites of the Bean \Vicia faba). 



The Bean Aphis {Aphis fabm, " black-fly," " col- 

 liers," etc.) is a member of a tribe almost entirely com- 

 posed of tte Aphides, or plant-lice. The Aphides are 

 all small animals furnisbed with six legs and a pair of 

 antennae, and usually with a pair of short tubes close to 

 the extremity of the abdomen, from which a clear sweet 

 secretion exudes. They all live upon plants, the juices 

 of which they suck, and when they occ,ur in great num- 

 bers cause serious damage to the crops, they attack. 



Both sexes are sometimes winged and sometimes wing- 

 less. "But the most singular portion of the history of 

 these insects is their very curious manner of propagation. 

 In the autumn, male and female insects are found, furn- 

 ished with perfect generative organs ; these copulate, 

 when the females lay eggs, which are hatched the follow- 

 ing spring. But, instead of producing individuals of both 

 sexes, these eggs give birth only to female insects, which 

 produce living young without any congress with the 

 male ; the brood thus brought forth again produces living 

 young in the same manner, and this goes on throughout 

 the whole summer, without the appearance of a single 

 male insect. In the autumn again, male and female in- 



