206 Choice of Plant Material 
dry soil, and its rate of growth will be in proportion to its 
feeding. Even the tolerance of shade is relative to the sup- 
ply of water. And as vigorous constitution fights off dis- 
ease, so, insect pests and fungus diseases attack the least 
vigorous, and hence in the last analysis are to some extent 
in relation to soil conditions. 
From what has been said, it stands to reason that all 
descriptions of form and statement of characteristics, unless 
more extended than can be given in this book, refer only to 
some stage of development and to typical trees and condi- 
tions, from which nature may deviate a hundred times. 
LIST OF TREES DESIRABLE FOR SHADE AND 
ORNAMENT 
While in office at Washington, the writer spent much of 
his leisure in becoming acquainted with the wealth of orna- 
mental material planted in the small parks of the city (some 
four hundred species). He caused to be compiled plats of 
all the parks and small places, locating each tree by number, 
so that at a glance, by reference to a numbered list, it could 
be named. There was also compiled, under his direction and 
personal supervision, a description of the species with such 
notes of interest as the tree-lover and tree-planter would 
appreciate. The manuscript, nearly completed ten years 
ago, when the writer left office, has unfortunately remained 
locked up in the drawers of the Department with which 
he had been connected, and failed so far of publication. 
The writer mentions this incident merely to justify his pre- 
suming to give advice on the choice of ornamental trees. 
The following list of nearly four hundred species and vari- 
eties does not in any sense pretend to be a complete enumera- 
tion of the trees which deserve attention, but it contains all 
