92 



THE HABITAT 



Koelera-Andropogon-psiiium 

 April 25, 1901. Clear. South wind. 



Querciis-Hicoria-hylium 

 April 20, 1901. Clear. Southeast wind. 



METHOD OF ECOGRAPH BATTERIES 



136. A battery of recording instruments consists of a selagraph, a psy- 

 chrograph, and a thermograph, to which an anemograph is added when pos- 

 sible. As stated before, the determination of water-content by the geotome 

 method is more satisfactory than by any automatic instrument yet devised. 

 When the base station is located where the sunlight is unobstructed, which 

 should be the case whenever jxjssible, it is unnecessary to include a sciagraph 

 in those batteries placed in similarly exposed stations, since the light values 

 will be the same. As a rule, batteries are established within different zones 

 or different habitats, except where a highly diversified habitat is made the 

 subject of special inquiry. Such a restriction arises from the fact that ex- 

 pense, care of operation, etc., place a limit upon the number of batteries, 



