METHOD OF SIMPLE INSTRUMENTS 89 



(3) northeast slope of ridge I, (4) grassyravine, (5) southwest slope of 

 ridge II, (6) bare crest of ridge II, (7) thicket ravine. The other series 

 was established in the bnr-oak-hickory forest {Qnercus-Hicoria-hylium) 

 at the following stations: (i) thicket, (2) woodland, (3) knoll in forest, 



(4) depression in forest, (5) level forest floor, (6) nettle thicket, (7) brook 

 bank. At Minnehaha the series was primarily one of different formations : 

 (i) the pine formation (Pinus-xcrohylium), (2) the gravel-slide formation 

 {Pseudocymoptenis-Mentzelia-chalicium), (3) east slope of spruce forest 

 (PicechPseudotsiiga-hylium), (4) ridge in the spruce forest, (5) north 

 slope of spruce forest, (6) brook bank in forest, (7) the thicket formation 

 (Querciis-Ccrcocarpus-lochmodinm), (8) the aspen formation (Popidus 

 hylitim). When permanent or temporary quadrats are established, they are 

 ordinarily used as regular stations, since this enables one to refer the 

 physical factor readings to a few definite individual plants, as well as to the 

 entire formation. The transects in figure 29 illustrate two of the above 

 series of stations. 



133. Time of readings. The frequency of simple readings and the 

 times at which they are made must be regulated largely by opportunity and 

 convenience. In addition to making readings once or twice a week through- 

 out the season, the series should be read at least once every day for a rep- 

 resentative week or two. It is also very desirable to have a series for each 

 hour of a typical day, or of two days, one of which is clear, the other cloudy. 

 When a single daily reading is made, it should be taken at or as near me- 

 ridian as possible. The usual series is the one obtained by simultaneous 

 observations at the same level in different stations. An important series is 

 also secured by simultaneous readings at the various levels of the same 

 station, though it is not necessary to take this series frequently. 



134. Details of the method. After the stations have been selected by a 

 careful preliminary survey of the habitat or series of habitats, their location 

 is indicated by a small flag bearing a number, in case there is no danger of 

 these being disturbed. Otherwise, less conspicuous stakes are used. The 

 ordinary practice is to visit each station of the series, and to take readings 

 of water-content, altitude, slope, and exposure. On the first trip these are 

 all made by the instructor, but after a short time the determination of each 

 factor may be assigned in rotation to each of the students. After these 

 constant factors have been read and recorded, one student is equipped with 

 photometer, thermometer, and psychrometer, and, if desirable, anemometer, 

 and left at the first station. At each succeeding station the same plan is 

 followed, so that at the end of the series the constant factors have all been 



