140 
W. B. Crump . 
nature of the problem, and in no way invalidating the concept of a 
constant quantity expressed by the mean ? If so what is the best 
method of deducing the mean value? On the other hand is there 
any unsuspected cause operating that can be detected and eliminated 
by mathematical analysis? In particular what is the cause for the 
water 
higher value of the \ -ratio in the case of the sub-peats? 
& humus 1 
It is clear, in the first place, that the range of water-content 
and humus-content is so great even when tiie sub-peats are separated 
from the peats that no great importance can be attached to their 
average values as expressed by the arithmetical means. Still it is 
noteworthy how closely the means in the case of the peats approxi¬ 
mate to the Rumbles Moor sample (No. 63) which is undoubtedly 
typical of the Yorkshire heather moor. 
Attention may therefore be concentrated on the values of the 
coefficient of humidity expressed by the ratio ^ 
water. 
umus. 
If for a given habitat 
water-content 
t -7—: — a constant 
humus-content 
we have simply a special case of the general equation of the straight 
line passing through the origin of rectangular co-ordinates x and y 
viz:— 
or y = mx . (1) 
where m=coefficient of humidity=tangent of the angle the line 
makes with the axis x. 
If the line does not pass through the origin the equation becomes 
y — b + mx . (2) 
where b is the ordinate at the origin. 
The points to be considered are whether the values set out in 
the last column of the tables conform to a straight line rather than 
some other curve; and if so, whether it satisfies equation (l)or (2), 
and then to find the value of m, and of b if required. 
When the values of x and y (humus and water) are plotted the 
the points obtained are so irregularly distributed that it is difficult 
to decide the slope of the curve by inspection, or*even whether it 
passes through the origin. But no curve other than a straight line 
corresponds with the points. So a trial may be made with a straight 
line drawn through the origin and making with the x axis an angle 
