I have recevd yours of yesterday and thank you for its prompt reply to my inquiries. I did not fully present my general idea, and in doing so partially, with reference to particular points, have a little misled you.

I am now thinking of a basin as extended (above grade 9) as practicable; the shores to vary much in character, sometimes sandy and beach like, [389] sometimes abrupt, sometimes and as much as can be afforded rocky; the bank above also variable, in degree of steepness, and to be, as a rule, overgrown thickly, in a picturesque, natural, completely informal even negligent manner, so that after a few years such slight damages as would occur (with the precautions I have in view) would at worst be inconspicuous. In my inquiry with respect to strictly tidal ground plants I had little reference to the foot of this bank, or to any islands which would bear trees or shrubs.

But I wish to avoid large areas of open water, and also, in order to spread the occasional floods over as much surface as possible and so avoid vertical rise of water to have large flats bearing vegetation which would tend to prevent the formation of waves.

I have large quantities of mud to be dredged and disposed of. I can form flats by making enclosures of solid earth and filling them with mud.

I shall have also large areas of mud and sedge bank already formed, the present surface of which, being several feet above the proposed high water level, must be pared down so that flood water may pass over it.

On these flats I can have a thin layer of any soil I choose and I can allow their surface to vary from a few inches above ordinary high water level to a few inches below ordinary low water level. Thus, as far as practicable, with a rise & fall of but one foot of tide, I can imitate the conditions in which any of the tidal ground plants best flourish. What I chiefly want is to be sure that I can perfectly cover these flats with marshy plants in considerable variety. There are a number of such plants which I know, and which I think could be used by planting sods of them, but upon all these I find myself in doubt as to the most suitable elevation having regard to a tide of one foot. I suppose that the “black grass” wants to be a little above ordinary high water. What I know as sedge (probably different species) grows both above and below this — in sand and in crevices of rocks. Whether it is soil or period of submergence that determines the position I don’t know.

There are many plants with which I have a general familiarity, as making pretty effects on the edges of tidal brackish water, which I fear might not grow where the water is as salt as it will be in the Backbay.

But in general I infer from your letter that without raising the surface of the flats more than a few inches above ordinary high water level I can have a large variety, including in the uppermost possibly certain Solidagos, asters [390] and bullrushes and lower the two or three plants which chiefly cover the marshes between Cambridge and Brighton.

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.

[391]

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

[392]

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.