Germunation of Forest Trees ng 
The germination of seeds depends principally upon edaphic 
factors, hence climatic factors will receive little attention here 
except in so far as they condition the former. It is taken for 
granted that the morphological and the physiological significance 
of water, light and heat to plant life are too well known to require 
discussion here, especially since that phase of botany is funda- 
mental in all ecological work. 
The water content of the soil is by all odds the most important 
edaphic factor in determining germination, for while other factors 
may condition this process to a certain extent, none but water, 
within certain limits, can prevent it altogether. In a synoptical 
manner I will briefly call to mind the significance of this master 
factor in germination and then briefly inquire into the important 
soil factors and properties that bear directly on the investigations 
at hand. 
The amount of water in the soil has no direct relation to the 
amount of water which plants can use. At the outset distinction 
must be made between the different kinds of water in the soil 
and which of these are available to plant roots. Usually three 
kinds of water are distinguished, namely: hygroscopic water, 
capillary water and free water. Hygroscopic water is that water 
which plants cannot get owing to the enormous film pressure 
which holds it. It is also known as the amount of water in an 
air-dry soil. Capillary water is that water, most of which is 
available to plants and is held against gravity around the soil 
particles by capillary forces. Free water is that which is not held 
either as hygroscopic or as capillary water. It is water influenced 
in its movements by gravity and is therefore called gravitational 
or hydrostatic water. Clements (1) calls these echard, chresard, 
and holard respectively. It will be seen then, that the only water 
available to plants is a part of the capillary water which surrounds 
every soil particle and fills every small pore space. 
The principal factors which influence the amount of soil mois- 
ture available (capillary water) to plants are: 
1. The amount of water reaching the soil. 
2. The catchment of water by the soil. 
3. The water-holding capacity of the soil. 
