Germination of Forest Trees Bs 
This principle is fundamental in mathematics; a single algebraic 
equation with two unknown quantities cannot be solved. In each 
of the series used in these investigations it was the intention to 
have only one variable habitat factor. In this way the study of 
cause and effect was much more clearly brought out. 
The soil moisture determinations were made for four different 
purposes : 
1. As acheck upon daily watering in similar cultures. 
2. To show the effect of shading on soil moisture content. 
3. To show the minimum content in the soil moisture series. 
4. To compare soil moisture content in loam, sand, and gravel. 
The samples were taken in certain cultures and at intervals 
varying with the purpose. The samples for the moisture content 
series of cultures were taken once a week, all others once a month. 
Each sample consisted of from 50-100 grams of soil, and was 
taken at depths varying with the development of the plants in the 
culture. In order to provide against error each sample consisted 
of from two to five portions taken from spots several decimeters 
apart, care being exercised that no soil was dug near holes where 
previous samples had recently been obtained. The samples were 
always dug between the rows of seedlings. The samples were 
immediately weighed and dried at a temperature of 95-105° 
Centigrade to constant weight (24 hours). The per cent. of 
water was computed upon the dry weight of the soil. 
All the cultures except the dry soil and the medium wet soil 
cultures were watered every evening. As was noted above, when 
the amount of room for the germination tests became insufficient 
the number of cultures was reduced from 12 to Io by eliminating 
two duplicate cultures. The only check moisture samples which 
will be considered here are those that have to do with the three 
cultures which were being operated under identical conditions. 
Samples taken and recorded hereafter will take care of the other 
cultures and series. During the time (three months) that these 
duplicate cultures were run, one set of soil samples was taken as 
a check to determine whether they were being watered equally. 
These figures follow: 
