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parative effects of the shades of different trees on vegetation, and 

 as I purpose to make use of the facts he has stated, in support of 

 what I have further to say on this subject, it will be necessary for 

 me to make considerable quotations from that paper. It is con- 

 tained in a letter to Dr. Mitchill in 1792— after some introductory 

 remarks he says — 



*' I shall be able to offer you nothing on the subject of experi- 

 mental husbandry that will merit your attention, unless it be an 

 observation which I have frequently made, but with more atten- 

 tion this year than before, and which may, I conceive, if properly 

 pursued, lead to important consequences. I mean the baleful ef- 

 fect of the shade (if I may so call it) of some trees upon the vege- 

 tation of corn. I will state the facts as they have appeared to me, 

 and you will the more readily comprehend my ideas. I planted 

 maize on the west side of a young wood, consisting of oaks, pop- 

 lars, a few chestnuts and a large mulberry, somewhat advanced in 

 the field. The shade made by the rising sun extended nearly 

 across the field and was not entirely off until about ten o'clock. 1 

 remarked that as far as the shade of the chestnut reached, the corn 

 was extremely injured, it was yellow and small : the conical shape of 

 the morning shade, from particular trees, might be traced to a consid- 

 erable extent, in the sickly appearance of the plants. The black 

 oaks were likewise injurious, but less so than the chestnuts, the 

 poplar was very little so. Near the mulberry tree, the corn was 

 covered by its shade for a very long time every morning, and 

 though not so large as that which had more sun, maintained a 

 healthy appearance. To what cause are we to attribute this phe- 

 nomenon ? It is certainly not the mere absence of light or heat, for 

 in this case the trees would have been equally injurious, or rather 

 the mulberry tree would have been the most so. It is not to any 

 dropping from the tree, for the corn grew under none but the mul- 

 berry. It is not to any effluvia from the trees, for this would either 

 be emitted in circles or wafted irregularly by the wind. Whereas 

 the shape of the shade was plainly traced on the corn. Were I 

 permitted to form a conjecture upon this extraordinary circum- 

 stance, I should conclude that the mischief was not occasioned by 

 the shade, but by those rays of light that actually passed through 

 the tree, either perforating the leaves (for none of them are per- 

 fectly opaque) or hdng brought in contact with thm, and that this 



