GRAMINEOUS CROPS. 121 



pre-anal segment is rounded. J. londinensis feeds upon 

 the roots and rootlets of wheat plants. 



Prevention and Cure. — (1) Green manuring with buck- 

 wheat destroys this pest. (2) Top-dressings of quicklime 

 or gas-lime also kill the wheat milliped. 



Trombidium trigonum is a small arachnoid or 

 "spider," and, on the authority of Curtis, injures the 

 spikes of corn, especially in France. On the other hand, 

 Mr. Walker and others in England assert that it feeds 

 upon the aphides that infest ears of corn, but does not 

 injure the corn. 



The Wheat Blight, or White Rust {Erysiphe 

 graminis), " forms a white superficial mildew on the 

 living stems and leaves of cereals and other grasses in the 

 summer and autumn." It has already been described in 

 chapters ii. and iv. 



The Smut Fungus (Ustilago carbo) has been de- 

 scribed in the present chapter ; " but how smut infects 

 loheat has long been a mystery. The spores ripen in the 

 young flowers, and have disappeared long before the grain 

 is mature. Attempts at infection of the grain or seedling 

 are almost always unsuccessful. . . . The experi- 

 ments of Jensen render it most probable that the plant is 

 infected by the spores while flowering, and that either the 

 ovum itself is entered by the mycelium, or that the spores 

 remain dormant in the grain until its germination, and 

 that then the parasite 'grows with the growth and 

 strengthens with the strength ' of the young plant " (Dr. 

 Scott). 



The Straw Mildew, or Blight, is the cause of a 

 well-known diseased condition of the stems of numerous 

 members of the Graminece (barley, rye, wheat, and 

 various grasses). The complete life-histoiy of the straw 



