THE WATER OF THE HABITAT 37 



results, it is advisable to take two or three complete sets of readings 

 in rapid succession. 



A complete set of habitat readings should be taken at least once 

 during the fall and winter respectively. A similar set of readings should 

 be taken just before the beginning of the growing period. After the 

 opening of spring, readings are taken once every week in connection 

 with the field study of the development and structure of the various 

 formations. Simultaneous readings through the different levels are of 

 the greatest value, and are the ones regularly made. Once during the 

 spring, however, it is arranged to have the class spend the whole day 

 in the field for the sake of ascertaining the hourly variation of the factors. 

 Likewise considerable value attaches to readings made simultaneously 

 in the different points of a single station, the stations being read suc- 

 cessively. Each student should enter all the readings made in his 

 record-book. Representative curves and combinations should also be 

 made and filed with the records. 



