CHAPTER XI. 
THE BLOOD OF TREES. 
Experiments in Connection with the Circulation of Sap in Trees.— 
Variety of Sap-exuding Trees.—Non Sap-yielding Species.—The 
Influence of Climate on Flow of Sap.—Composition of Sap, to What 
Due. — Distinctive Characteristics of Sap-yielding Trees Demon- 
strated.—Effect of the Temperature of Soil and Atmosphere on Sap- 
flow.—Principal Ingredients of Sap.—Daily Meteorological Obser- 
vations and What they Prove.—Explanations on the Alternations of 
Sap-flow.—The Observations of Biot and Nevins, and What they 
Determine.—The Opinion of Mr. Hubbard Confirmed by Experi- 
ments.—The Absorbent Power of Roots.—Development of Leaf 
and Flower, How Influenced, and Origin of their Vitality. 
A series of experiments made by Professor W. 8S. 
Clarke, President of the Massachusetts Agricultural Col- 
lege, throws much light on a subject which has hitherto 
remained in great obscurity—the circulation of sap in 
trees—and promises an understanding of many things 
connected with pruning and transplanting which have 
hitherto been veiled in obscurity. Unable, from want 
of space, to present our readers with the full report, we 
endeavor to condense the material portions into a brief 
space. The familiar facts—that sap flows from wounds in 
certain trees in the spring, that from the sap of the maple 
sugar is obtained, and that the peculiarities of the season 
affect the quality and quantity of the flow, suggested 
these experiments, whose object was to determine the 
amount, pressure, and composition of sap which might be 
obtained from different species of woody oxogens. The 
great majority of trees and shrubs, it was found, do not 
at any season of the year bleed from wounds in the wood, 
and but few of the species which, in our northern lati- 
