Scientific students of the subject are divided between two theories of the nature of malarial poison, and differ as to the manner in which trees act upon it, but the following propositions satisfy either theory, and their soundness is, I believe, unquestioned.

1st. If malarial poison originates in a particular locality, and there is a free movement of air between the locality and a hill a mile away from it in the direction in which the prevailing winds of summer move, the poison is likely to be more felt upon the upper part of that hill than in the intermediate valley.

2d. But if there is a belt of trees crossing the direct line between the two localities the entire higher ground to leeward is often found to be wholly, and nearly always partially and in an important degree, protected from the action of the poison.

If, therefore, there was a body of trees along the base of Capitol Hill, the ground beneath them being well drained and not in itself adapted to the production of malaria, it would in all probability be an efficient means of protection to the Capitol from malarial poison originating on the banks of the Potomac and in the low grounds between the river and the hill.

Your suggestion that a plantation for this purpose could be formed upon the government property along the line of the old canal seems to me an excellent one.

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Plan for tree planting along line of old canal between Independence Avenue and Reservation 17

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I have attempted to give it a more definite form in the accompanying map, by which it will be seen that while maintaining with unimportant exceptions the existing and intended lines of public communication, a continuous belt 160 feet wide could be planted so as to connect the existing plantations of the Botanic Garden with another to be formed upon reservation 17. I have proposed a walk 20 feet wide through the middle of the belt, as the branches of the trees standing at its sides would soon meet overhead and form an unbroken body of foliage. I think it desirable to avoid so large a gap as would be needed for a central drive and walks.

The desired result would of course be much sooner and more effectively obtained if the plantation could be extended over the space between the proposed belt and the Capitol grounds, and this would give a much needed opportunity for enlarging the collections of the National Botanic Garden, and add greatly to the dignity of the Capitol itself.

But the suggestion could be carried out as indicated on the map without the purchase of any land, at very moderate outlay for soil, trees, and planting, and with confidence in results of value to Congress and to the public.