1922] HARVEY—PINE FORMATION 33 
Fig. 5 is an attempt to exhibit to scale the soil-water relations 
in the Big Pines formation as they existed in August 1918. That 
the data may be comparable they are all computed on the basis of 
dry weight. The critical factor is the growth-water, whose theoreti- 
cal possible maximum would be the difference between the WC 
and the WHC, or 29 percent. This of course would scarcely ever 
be realized under field conditions. Actually the growth-water is 
the difference between the TFC and the WC, which in August 
1918 was only 1.5 per cent, a quantity dangerously near the zero 
point of available water. 
EVAPoRATION.—The evaporation data were obtained in the 
usual way, Livingston standardized 8 cm. atmometers being used. 
During the month 284 mm. of rain fell on seven days, 250 mm. of 
wHe = 33 % <— 
peli tee Possible growthewater = 29% € 
Fic. 5.—Soil-water relations (shown to scale): data on basis of dry weight. 
this falling in twenty minutes. Rain correcting atmometers were 
not available, but it is thought that the use of these would not have 
given essentially different results. For five of the stations the 
records were taken daily; for the others every seven days. The 
250 cc. reservoir bottles were all set slightly in the ground and 
stabilized with 12 inch length of ;8; inch mile steel to which they 
were bound by two bands of electric tape. Readings were made 
on an index mark on the neck of the bottle, and loss of water was 
supplied from a 50 cc. burette. Distilled water was used through- 
out. Stations were selected to represent various conditions of 
cover and canopy. The results are tabulated in table ITI. 
The records in table III give evaporation rates only for the 
low herbaceous layer, and the. average daily range from 8.3 to 
18.6 cc. (124 per cent) is solely an expression of the degree of 
exposure, varying directly with the amount of insolation afforded 
by the herbaceous and shrubby layer. In connection with the 
