THE BLOOD OF TREES. 51 
spout yielded six pounds of sap, the limb two ounces, 
and the upper spout none at all. Similar experiments 
of other trees showed the flows of sap to be most free 
within twelve feet of the earth, diminishing rapidly 
above that height. Experiments upon the roots proved 
that the sap flowed from both ends of a cut root, and 
that it all contained sugar. 
The largest flow noticed during any one spring day 
was from a healthy shade-tree, six feet five inches in cir- 
cumference, March 23, and amounted to ten pounds and 
three ounces. Sap gathered from the latter tree Novem- 
ber 7 was found to contain only half as much sugar as 
that obtained in March from the first tree. Mr. Hub- 
bard, an experienced sugar-maker, is of the opinion that 
the amount of sugar obtained from a single tree can- 
not be augmented much by multiplying the number of 
spouts. 
Two half-inch holes about two inches deep suffice for 
ordinary trees, while four spouts and two buckets are 
used for very large trees. The average annual product 
of the sugar maple varies from twelve to twenty-four 
gallons of sap, yielding from two to three pounds of 
sugar, though the yield of a single tree is said to have 
exceeded thirty pounds in one season. 
Birches seem to exceed all other trees in the amount 
of sap which they yield—black, yellow, paper, and gray 
or white birch were tested and reached the maximum 
of fifteen pounds per day per spout. They were tapped 
March 19,.commenced yielding on the 25th, and ended 
the last of April. 
At six o’clock, a.m., April 2, the two gauges in a black 
birch—the first at the ground and the second thirty feet 
higher up—indicated respectively pressures of 56.65 and 
26.74 feet of water, the difference corresponding almost 
exactly to the difference in height. A hole being bored 
at 12.30 p.m. opposite the lower gauge, the pressure fell 
in fifteen minutes equal to 10.27 feet of water. Upon 
