74 
THE ESSEX NATURALIST. 
lovers would lose should an artificial system of drainage ever 
be developed. 
During the great drought of 1921, it was evident that these 
gravels had considerable capacity for retaining large quantities 
of water. In the report of the excursion secretary to the Quekett 
Microscopical Club, 1921, the statement occurs that, on that 
Club’s visit to Chingford and Strawberry Hill on 25th J une, the 
pond on Chingford Plain was dry, but that by the Earl’s 
path contained water, as did the pond at Goldings Hill. These 
examples were characteristic of the ponds throughout the 
Forest: those on clay were dried up, those on the plateau gravel 
below the 300 contour contained water at the end of the long 
drought. 
The prevalence of birch on light soils and its absence from the 
clay, indicated above, refer here solely to the Forest, for birches 
are known to grow on nearly every kind of soil. Warming 
gives a whole series of Danish birch types, from that on peat 
with Calluna and Vaccinium, to birch with meadow grass 
underneath. In a communication from Dr. W. G. Smith he 
writes, “ I know it (the birch) from the surface of 15 feet of peat 
on the Humber to the stony slopes of our Scottish hills.” There 
are a few birches on boggy ground at the head of streams that 
run through Hangboy and other Slades, but the water in these 
bogs is never quite stagnant. 
Samples of soil taken at depths of 1.5", 4.5", 6.0" and 10.o y 
were forwarded to Dr. E. J. Salisbury, who has published the 
accompanying graphs illustrating hydrogen-ion concentration 
and the percentage of humus. They show that the organic 
content decreases rapidly with increasing depth, and that the 
hydrogen-ion concentration attains its maximum at the surface. 
The sample from Piercing Hill is not quite normal; there man 
has interfered by planting Pinus sylvestris. 
The fruit of the birch Betula alba is small and light in weight. 
It consists of a narrow nutlet with an average length of 2.5 mm., 
while its width, including the membranous wings, approximates 
4 mm. The average weight of a fruit is 0.00023 grams. From 
the size of the nutlet and the breadth of the wings one realizes 
that a fruit, once lifted by the wind above the height of the 
surrounding trees, may be carried for a great distance during 
a heavy gale of wind, yet it is a common sight to see the ground 
