78 FLORIDA GEOLOGICAL SURVEY-I3TH ANNUAL REPORT

 In each region described the principal vegetation types (which are discussed more fully in the general part of the report) are indicated, and the commonest large trees (i.e.., those large enough to be sawn into lumber), small trees, woody vines, shrubs and herbs are listed as nearly as possible in order of abundance; which besides bringing out the general appearance of the vegetation also shows at once each region's resources in timber and other wild products of the vegetable kingdom. There are of course all gradations between trees and shrubs, and a species which is a small tree in one region may be a large tree or a shrub in another, or even in different habitats in the same region. But although no hard and fast lines can be drawn, some sort of size grouping has to be used, for it is impracticable to compare the relative abundance of plants differing greatly in size, such as trees and grasses. Mosses, lichens, fungi, etc., are omitted entirely, partly because they form such an insignificant fraction of the total bulk of vegetation, and also because only a few specialists (of whom the writer is not one) can identify them positively in the field.
 It did not seem worth while to assign percentages to nearly all the species, as was done in the northern Florida report, on account of the incompleteness of the data, but in the general discussion there is a census of timber trees, giving within certain limits the proportion that each is supposed to constitute of the total forest of each region. And the percentage of evergreens in each region has been estimated, as before, for that being made up of figures for a number of species is more accurate than the percentage of any one species The significance of evergreens is that, other things being equal. they are most abundant on the poorest soils-, for a tree growing in very poor soil has difficulty in getting enough nourishment to make a complete sei of leaves every year, and is almost obliged to keel) each leaf two or more years (sometimes a dozen years in the case of some of the spruces of the far north, where the soil is frozen about half the year) while a tree in rich soil may take up mineral matter in solution so fast that it has to have large leaves to store the surplus in and shed them every year to get rid of it*

 *For additional notes on the relation of evergreens to soils see 6th Ann. Rep. Fla. Geol. Surv., 175-177 (footnote): Science II. 42:500-503. Oct. 8, 1915: Bull. Geog. Soc. Phila. 16:Ti1. Dec. 1918; Geol. Stirv. Ala. Special Rep. No.
 11, p. 90, 1920.