May, 1908.] Annual Wood-Increment of Acer rubrum L. 
345 
These frequency distributions are shown graphically in 
Fig. 1. The abscissae give width in millimeters, the ordinates 
frequencies of rings. The variation constants deduced from 
them are indicated on page 347. 
For the benefit of those unfamiliar with the biometric method 
of study employed here, a brief discussion of the more salient 
points is appended. For a more complete statement the reader 
is referred to Davenport’s “Statistical Methods’’ (4) or the 
more popular work of Pearson (6). 
Fig. 1 —Frequency curves showing variation in width of the annual wood- 
increment in Acer rubrum. Continuous lines—bog habitat; Dotted 
lines—woodlot habi;at. 
It will be noted that in the trees of the bog habitat, there 
are more rings three mm. long than of any other length, 
while in the second type of habitat the greater number of rings 
has shown two mm. This highest frequency or most common 
length is known as the mode. It shows clearly the prevailing 
type of wood-accretion. The distribution decreases in both 
directions from the mode, but least so in the woodlot habitat. 
The practical importance of the information afforded by this 
value is apparent. We have here the average prevailing state 
or place-habit of a similar lot of individuals from two distinct 
places. It is a characteristic which has been determined by 
influences covering a period of time (the age of the trees) long 
enough to eliminate the effect of incidental fluctuations in the 
