76 



THE HABITAT 



can be made without serious inconvenience. The reading of the register- 

 ing dials requires detailed explanation, and for this the reader is referred 

 to the printed directions which accompany the instrument. In setting up 

 the anemometer it must be borne in mind that the ecologist desires the wind 

 velocity for. a particular habitat. In consequence, the precautions which the 

 meteorologist takes to place the instrument at a certain height and well 

 away from surrounding obstructions do not hold here. Standard anemo- 

 meters are furnished by H. J. Green, and J. P. Friez for $25 each. 



The anemograph is an anemometer electrically connected with an auto- 

 matic register. It is the only instrument adapted to continuous weekly 

 records in different habitats, but the price, $75 ($25 for the anemometer 

 and $50 for the register) is practically prohibitive, at least until a complete 

 series of ecographs for other factors has been obtained. 



110. Records. The following form is used as a combined record for 

 precipitation and wind: 



SOIL 



111. Soil as a factor. In determining the value of the soil as a factor in 

 a particular habitat, it must be clearly recognized that its importance lies 

 solely in the control which it exerts upon water-content and nutrient-con- 

 tent. The former is directly connected with the texture or fineness of the 

 soil, the latter with its chemical nature. Accordingly, the structure of the 

 soil and its chemical composition are the fundamental points of attack. 

 These are not at all of equal value, however. Water is both a food, and a 

 solvent for the nutrient salts of the soil. Furthermore, the per cent of sol- 

 uble salts, as determined in mechanical analyses, is practically the same for 

 all ordinary soils. Indeed, the variations for the same soil types are as 

 great as for entirely different types. For these reasons, soluble salt-con- 

 tent may be ignored except where it is readily seen to be excessive, as in 

 alkaline s6ils ; and determinations of chemical composition are necessary 

 only in those soils which contain salts or acids to an injurious degree, e. g., 



