1847.] Hessian Fly. 105 



most familiar, are enveloped in a kind of mystery, and hence be- 

 yond his reach. He can, however, bring out the phenomena of 

 vegetation in its season; the grass and grain springs up when he 

 sows the seed; it grows up under his eye, though not in obedience 

 to his will; he still stands, however, in the place of its proximate 

 cause. He has learned by ample experience that its growth may 

 be promoted or retarded by certain agents; yet the why and the 

 wherefore he has not satisfactorily determined. 



HESSIAN FLY. 



Dr. Emmons — Since ray return from my very delightful excursion 

 through your state, I have renewed my researches in the wheat 

 fields, and have been partially successful, though not equal to my 

 expectation. From some cause, which I cannot explain, the larvae 

 of the Cecidomyia which I have found feeding in the centre of the 

 straw, have been so retarded in their growth that they have not 

 attained more than half their usual size. While the wheat is ready 

 for the harvest, of course there are none on the outside of the 

 straw, and no injury appears to have been done in the grain, though 

 the worm is to be found in great abundance through the field that I 

 have been in the habit of visiting. What will be the result I am 

 unable to conjecture, but intend to bring a sheaf of the wheat, 

 when cut, into the library, and thus have it under daily inspec- 

 tion. Perhaps the larva may not perish, but go through their 

 changes inside the straw, though I fear Ihey will, as they usually- 

 pass through their different changes in time for the flies to deposit 

 their eggs on the grain while in the soft or milky state. 



I have gathered some of the straws with the larvae in them, for 

 you, and leave them in the care of Prof W. R. Johnson, who 

 will, I have no doubt, forward them to you. Together with these, 

 I send another insect, the larva? of which I found feeding in the 

 earth of a flower-pot in my window. Desirous of ascertaining 

 its true history, I put some of the earth containing larva; and pu- 

 pae under a bell glass, in which I planted a bunch of growing 

 wheat, suspecting it to be a wheat fly of some kind. In two 

 days a number of flies made their appearance, and on the third, I 

 saw six flies depositing their eggs on the lowest leaves and sheath 

 of the growing wheat. At first these eggs were of a pale straw 

 color and nearly transparent, but subsequently became black; they 

 are firmly glued to the straw, and have undergone no change 

 since then, from which I infer that the earth is their feeding place, 

 and their food the decaying straw. If so, they must be useful in 

 hastening the decomposition of the straw, and rendering it sooner 

 available for manure. 



