26 
tho 5-ycur seedlings of sugar maple* Balsam seedlings wore 
found in the suimier parts of the quadrat, Zb individuals 
being counted* Several species of moss, already mentioned, 
were found on rotting logs in or near this quadrat* They are 
often of considerable ecological importance in the formation 
of seod beds* 
In tho quadrat studies above described, certain 
conclusions in regard to shade tolerance and its effect in 
the distribution of the species, seem inevitable* This will 
bo considered in what follows* 
3. IUITIiiL PHYSICAL FACTORS AND COMPETITION. 
I<; is evident that a great many factors enter in 
to the dynamics of the forest* a few of those have been 
pointed out as thoy affect the life history and occurrence 
of the dominant species of troes* In a consideration of the 
composition of the hemlock climax on the north slopo, two 
questions arise* First, what cutises tho variation in com¬ 
position from tho base of tho elope to tho top of the ridgo, 
a difference in elevation of approximately 300 m.? Second, 
what is the most effective factor governing tho composition at 
any one point? Frothingham has pointed out that there are 
two sets of factors influencing the distribution and dominance 
of trees in tho natural forest, namely, physical , including 
soil, humidity, li^ht, etc. and physiological (biotic) including 
