PLATE 23 
A. —Method of measuring the penetration of water in three zones of a ring of 
Agaricus tabularis. The first three 2-liter flasks in the foreground are in the bare zone, 
the second three are in the withered zone, and the three in the background are out¬ 
side. Those in the bare and withered zones are still almost full of water while those 
outside in the natural sod are empty. Akron, Colo., July 13, 1916. 
B. —A ring of Agaricus arvensis showing the effect of irrigation during a dry year 
on the different zones. At this period the vegetation both in the zones of the ring 
and in the native sod was entirely dormant, due to drouth. On this account the 
withered zone could not be distinguished from the other vegetation. The effect of 
the surface flooding was marked between the lines C and D. The outer edge of the 
bare zone is marked by the line A and the outside of the irrigated area by the line B. 
The area 3 represents the bare zone during a dry year and was in the same condition 
as that of area 1 at the beginning of the experiment. The effect of irrigation on the 
natural sod is shown by comparing area 2 with area 4. It is clear that, although the 
vegetation in area 3 was dying out owing to drouth, if water was continually supplied 
in quantities sufficient to keep the surface soil continually moist the grasses and other 
plants grew luxuriantly, indicating that the chief cause of the death of the vegeta¬ 
tion was the deficiency in soil moisture. In the background of areas 1 and 2 is shown 
the trench illustrated in Plate 20, A. Akron, Colo., August 14, 1916. 
