WATER-CONTENT 29 
base already exists, or, better, while it is being established, scattered readings 
may be used somewhat profitably. As a practical working rule, however, 
it is most convenient and satisfactory to make all determinations consecu- 
tively, i. e., in a series of stations or of successive days. Under ordinary 
conditions, the time of day at which a particular sample is taken is of lit- 
tle importance, as the variation during a day is usually slight. This does 
not hold for exposed wet soils, and especially for soils which have just been 
wetted by rains. In all comparative series, however, the samples should be 
taken at the same hour whenever possible. This is particularly necessary 
when it is desired to ascertain the daily decrease of water-content in the 
same spot. In the case of a series of stations, these should be read always 
in the same order, at the same time of day, and as rapidly as possible. When 
a daily station series is being run, i. e., a series by days and stations both, 
the daily reading for each place should fall at the same time. While there 
are certain advantages in making readings either early or late in the day, 
they may be made at any time if the above precautions are followed. 
47. Location of readings. Samples should invariably be taken in spots 
which are both typical and normal, especially when they are to be used as 
representative of a particular area or habitat. A slight change in slope, soil- 
composition, in the amount of dead or living cover, etc., will produce con- 
siderable change in the amount of water present. Where habitat and 
formation are uniform, fewer precautions are necessary. This is a rare cir- 
cumstance, and as a rule determinations must be made wherever appreciable 
differences are in evidence. The problem is simpler when readings are taken 
with reference to the structure or modifications of a particular species, but 
even here, check-readings in several places are of great value. The varia- 
tion of water in-a spot apparently uniform has been found to be slight in the 
prairies and the mountains. In taking three samples in spots a few inches to 
several feet apart, the difference in the amount of water has rarely ex- 
ceeded 1 per cent, which is practically negligible. Gardner! found that 16 
samples taken to a depth of 3 inches, in as many different portions of a 
carefully prepared, denuded soil plot, showed a variation of 7% per cent. 
This is partially explained by the shallowness of the samples, but even then 
the results of the two investigations are in serious conflict and indicate that 
the question needs especial study. It should be further pointed out that all 
readings should be made well within a particular area, and not near its 
edge, and that, in the case of large diversified habitats, it is the consocies 
and the society which indicate the obvious variations in the structure of 
the habitat. 
1GARDNER, F. D. The Electrical Methods of Moisture Determination in Soils. 
Bull. Div. Soils, 12:12. 1898. 
