Medication
It is only a step from the consideration of nutrition of a plant or animal to that of medication. Remedial agents are readily introduced into plants, either through the roots, or by spray on the foliage, or by direct injection into the trees. Going a little further, such methods become means of killing trees.
A few years ago, I became interested in killing trees in a way which would prevent sprouting and also protect the wood to some extent from insect attack and decay organisms. More recently my interest has turned toward the use of hygroscopic chemicals injected in the living tree for the purpose, not only of killing the tree, but of preventing the wood from cracking radially or drying. A number of government publications[4-10] have contributed information along this line.
To inject enough chemical to accomplish this purpose it seems necessary to introduce the chemical solution through a cut the depth of the sap wood and extending entirely around the tree. A collar of water-proof paper cemented to the tree provides a means of supplying the chemical solution to the cut. All this is described in the literature cited. The only contribution I have made is the use of urea in the solutions.
Many salts are more soluble in a water solution of urea than in water alone, and many such mixtures are very hygroscopic. Moreover, it seems that in the presence of urea higher concentrations of salt may be introduced into the sap stream of trees, though I do not as yet have experimental data to confirm this statement quantitatively.
An example of a solution injected into a small ash tree is as follows:
90 grams urea
120 grams copper sulfate crystals
300 cubic centimeters water
I hope in another year to cure a number of varieties of woods on the stump and later to compare their qualities in the shop with lumber cured in the usual way.