KESEAKCH METHODS IN STUDY OE FOREST ENVIRONMENT. 141 
(b) Selection of the soil sample at the point of maximum moisture 
content within the zone reached, which, of course, in the important 
periods of drought, will usually be the deepest point reached. 
(c) Determination of whole moisture of each sample. 
(d) Determination of moisture equivalent of each sample, at least 
as a means for classification of unlike samples. 
(e) Eetention of samples, with determinations of wilting coeffi- 
cients on typical classes, probably after the period of field observa- 
tions. In these determinations it will be well to compare the be- 
haviors of the two or more species involved. 
It is believed that, with tiny seedlings, the quantity of water 
usually required to maintain life is so small that the available volume 
may be left out of consideration. In other words, the samples may 
be practically point samples, seeking always the maximum available. 
Even this painstaking examination of soil moisture, however, may 
be futile without a record of the conditions conducive to water loss, 
particularly the temperature conditions at the surface of the soil. 
15. Whenever, in a plant society, competition between individuals 
of the same or different species becomes a factor, the moisture prob- 
lem is different from that which confronts seedlings. In the forest 
there may be competition for moisture without keen competition for 
light, but the two will usually be closely interrelated. In any ordi- 
nary situation the keenest competition for moisture occurs near the 
end of the growing season, when the reserve winter moisture has 
been exhausted and the current rate of use is in excess of the current 
accretion. Where this is the case the study of soil moisture may be 
restricted to a period of two or three months in the late part of the 
season. 
It is evident that, of two individuals on the same site, one may 
possess an advantage over the other through deeper rooting. It is 
therefore essential in each site studied to know the extent and depth 
of the roots of the plants under observation, and to sample the soil 
for moisture in accordance with a root map. 
If it should appear that two individuals in competition have essen- 
tially the same moisture supply, then it obviously becomes necessary 
to determine their respective relations to that supply by examination 
of their internal conditions as affected by atmospheric conditions, 
light, etc. It is not sufficient in these circumstances to say that soil 
moisture is not a factor in the greater success of one than of the 
other. By measuring the osmotic pressures of the plants it may be 
found, for example, that the individual which is most exposed to 
light, wind, and other desiccating influences has a greater control 
over soil moisture than the near-by individual which is shaded 
and protected, and which, nevertheless, may die from the effects of 
