Development of the Vegetation of New York State 171 
consider primarily the dominating forms, i. e., the trees with 
direct light exposure whose crown canopy is the chief factor 
in bringing about the differentiated light relations of the for- 
est environment and in creating special atmospheric condi- 
tions (still, moist, cool air, reduced evaporation from the 
forest floor, disposition of rainfall, ete.) —items not pe- 
culiar, of course, to climax forest. A train of consequences 
follows the shutting off of direct light by the forest crown: 
in degrees of shade tolerance from the subordinate trees 
down to the members of the lowest stratum (mosses, liver- 
worts, etc.) ; in habit, rate and form of growth of stems, size 
and structure of leaves, time of flowering, leafing, fruit 
ripening, seed dispersal, ete. The distribution of roots with 
respect to utilization of soil moisture and soil nutrients by 
the various associates of the forest may be considered as a 
noteworthy item under growth relations. Perhaps here, also, 
may be mentioned the forest floor species —trilliums and 
other liliaceze, Jack-in-the-pulpit, wild ginger, pepper root, 
squirrel corn and the whole list of forest favorites whose per- 
ennial parts lie imbedded in the leaf mold or duff blanket and 
find therein congenial soil for vegetative propagation. The 
mat forming habits of mosses express features of growth 
relation of significance for the forest community (e. g. in 
the taking up and retention of moisture). The réle of bac- 
teria, forest soil fungi and wood destroying fungi has already 
been emphasized in connection with the removal of the men- 
ace of accumulating dead members or parts of the forest 
community and the transformation of these into available 
productive energy. This, of course, expresses most signifi- 
eant growth relations (notably saprophytism). Again, the 
phenomena of parasitism of fungi in general, but notably 
such eases as beech drops and broom rapes parasitic on the 
roots of forest trees. Finally, as perhaps the most unique 
aspect of growth relations, significant too in its social bear- 
ing, should be mentioned the phenomena of symbiosis as be- 
tween fungi and the roots of forest trees (mycorhiza, my- 
cosymbiosis), which is shown to be of rather general occur- 
