52 PRIZE essay: 



absence of silica seems to be the chief cause of its liability to 

 be broken by agitation. 



82. The underbill wheat, so long cultivated and celebrated for 

 its immunity from the attacks of the Hessian fly, affords an 

 admirable instance of the silicious shield of the wheat stem re- 

 sisting the attacks of the fly. Those varieties of wheat which 

 produce strong flinty stalks have long been known not to suffer 

 much injury from the presence of the spring maggot. The na- 

 tural tendency of these varieties to assimilate large quantities of 

 silica, enables them to withstand the weakening effect due to the 

 insect, under which other varieties, naturally less rich in silica, 

 would succumb. 



83. The preceding remarks refer solely to the injury caused 

 to the wheat plant by the weakening of the stem, and its frac- 

 ture before arriving at maturity. It is to be observed, however, 

 that the presence of two or more of the spring larvae of the 

 Hessian fly must operate very disadvantageously in other res- 

 pects. On thin-stemmed varieties the growth of infected stems is 

 often altogether arrested by fracture, if the maggot descends to 

 itsseat above thefirst or second joint before the plant has acquired 

 a strong and healthy growth, and under such circumstances 

 the field has been very appropriately likened to one through 

 which a herd of cattle had been making their way. 



84. Since the injury occasioned by the larvae of both broods 

 of the Hessian fly is produced in the first instance upon the stem, 

 whether above the crown of the root in young wheat, or at the first, 

 secondorthird jointof thatwhich is farther advanced, itnecessarily 

 follows that a more or less healthy condition of those parts of 

 the plant will enable it to resist to a corresponding degree, the 

 attacks of the insect. A strong and vigorous tillering growth 

 in the fall (m) and spring is required to maintain a condition of 

 comparative health under the attacks of one or two of these para- 



