1918] HUTCHINSON—FOREST TREES 471 
phytic, as Fagus and Acer. It seems possible that there might be 
a similar range amongst conifers. Zon (27) states, “Balsam fir 
attains its best growth and largest size on flats the soil of which is 
usually a moist, deep sand-loam.”” An abundance of available soil 
water is not the factor which so often excludes Abies balsamea 
from such soils, particularly in the more temperate regions. 
During the summer of 1914 a series of experiments were con- 
ducted in Algonquin Park to discover the relation of seedling 
growth to atmospheric humidity. Atmometers of the Lrvincston 
design were set up at a number of stations, including those where 
seedlings of Acer saccharum, Abies balsamea, and Picea mariana 
were abundant. The readings for the months of July, August, and 
part of September proved that in this region there is no appreciable 
difference in the rates of evaporation at the stations mentioned, 
and that in each case the humidity was in excess of that which 
FULLER (13) regards as characteristic of a mesophytic forest. 
Moreover, Acer grows on the more exposed ridges; Abies and 
Picea on the less exposed lowlands or slopes. Experiment has 
shown that such conditions hold generally for the “lake country,” 
where in many cases one-tenth of the total area is covered by water, 
and the greatest distance of any point from bodies of water seldom 
exceeds 2 miles. Three of the limiting factors most frequently 
emphasized, temperature, atmospheric humidity, and precipitation, 
are eliminated, as such, under conditions prevailing, and still there 
is a marked segregation of forest associations. 
Soil factor 
The problem regarding the extent to which soil cpmposition 
may act as a limiting factor in the determination of forest dis- 
tribution has been variously answered. FROTHINGHAM (12) 
states “The soils of the northern hardwood forest are as a rule 
loamy sands, the results of the decay of granite, quartzites, and 
siliceous gneisses, also the water assorted loams and clays or the 
unassorted morainal tills, rich in clay; but they also thrive on light 
sandy soil in localities subject to moist winds.” In connection 
with the forests of Michigan, BEAL and WHEELER (1) state that 
“The best wheat lands are usually found on uplands near 
