RESEARCH METHODS IN STUDY OF FOREST ENVIRONMENT. 141 



(6) 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) Retention 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 

 maybe 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 measurmg 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 



