Development of the Vegetation of New York State 87 
migrate farther up State because the climate becomes too 
severe once you are out of range of modifying ocean influ- 
ence. Nevertheless, some horticulturist may take these 
very species and grow them, say, at Rochester. Practical 
experience (experimentation re eally) is showing repeatedly 
how elastic the temperature boundaries are if only the 
species has the most favorable conditions for nutrition and 
growth so far as the soil is concerned. In this connection 
the northern extension of that large lst of forest floor 
species to which attention was called on page 73 whose 
perennial parts lie buried over winter in the blanket-lke 
cover of leaf mold under the leaf mulch of the last leaf 
fall, may be suggestive. Cultivation results appear to 
show that, in nature, species often are kept at a point 
notably below their possible efficiency in growth, fecundity 
and ground gaining ability, i. e. capacity to occupy a wider 
range, by a combination of factors which, whatever they may 
be, are not referable to climatic temperatures. Of course, 
under cultivation, selection begins to play a réle in elimina- 
ting mediocrity. 
In this discussion, however, the relation of vegetation to 
chmatic and soil factors has been considered separately 
because it seemed that the main idea of showing the 
developmental history of vegetation could best be brought 
out in that way. So let us take it that we have followed 
the migration of a flora into a new region and the segre- 
gation of floristic elements into certain climatic relations 
of fixed character, and now we are ready to go into the more 
local matters of segregation of species and growth forms 
into associations or societies as determined chiefly by the 
nature of the substratum in and upon which they grow. 
Most important of all we wish to show the effects upon the 
substratum of this work of a vegetation cover and how 
thereby the different associations are brought into a develop- 
mental relation to one another so that the history reads as a 
sequence of development leading up to a highly organized, 
permanent or equilibrium stage of vegetation — the climax 
forest. 
