THE HESSIAN FLY. 51 



In the preceding diagram the right-hand shoot is represented 

 as withered and lifeless from the attacks of the maggot at the 

 crown of the root under the suface of the soil. The left hand 

 stem is free from any attack and consequently uninjured. The 

 process of tillering would throw out a number of new shoots 

 from the crown of the root to replace those which are des- 

 troyed. 



81. The maggots appear to live wholly by suction. They do 

 not penetrate the stem, or make any apparent incision ; they 

 produce, however, a depression, caused by the obstruction they 

 offer to the growth of that part of the plant where they are 

 seated. These depressions, though not always apparent on the 

 outside, when produced by several maggots of the second brood 

 in the early summer months on the first or second joint, greatly 

 weaken the stem, and render it liable to be blown down and 

 broken by a light breeze of wind, when it has attained the attitude 

 it acquires on approaching maturity. Sometimes a swelling or gall 

 is the result of the attack as shown at ( ) in Fig. B, page 56, 

 (paragraph 92.) 



81. The manner in which the maggot of the spring brood 

 affects the stem in the early summer months, seems to arise from 

 its presence preventing the deposition of the necessary amount 

 of silica or flint immediately under its body. It is well known 

 that the great strength of the hollow cylindrical stem of the 

 wheat plant is due to the large amount of silica it contains, and 

 where there is a deficiency of this strenthening material, the 

 stalk is unable to support the weight of the ear when agitated 

 by wind ; were the usual quantity of silica present the small re- 

 duction in the diameter or dimension of the stalk (supposing no 

 gall to be formed) at the point where one or more of the maggots 

 are seated would not materially interfere with its strength. The 



