WATER GAUGES. 249 



mon exogenous trees, and, while none of the observations can 

 be exactly repeated from the nature of the phenomena, yet 

 they may safely be accepted as the substantial truth concern- 

 ing the whole subject. 



The interesting tacts observed last year, in connection with 

 the attachment of mercurial gauges to the roots and trunks of 

 trees which were known to bleed from wounds, and the sug- 

 gestions derived from them, were a powerful stimulus to fur- 

 ther investigations in this direction. Accordingly, a large 

 number of gauges were prepared in early spring, and, as soon 

 as the weather was suitable, attached to such trees and roots 

 as gave promise of the most valuable results. 



There still remained the unaccountable fact that the larger 

 number of trees and shrubs did not show any tendency to 

 bleed in spring, and therefore could not be made to answer 

 any inquiries put to them in regard to the circulation of sap. 

 It was thought best to adopt a cheaper and simpler form of 

 gauge for application to such species as gave small promise of 

 useful results. For this purpose, the following economical 

 apparatus was devised and applied to the roots of elm, ash, 

 white oak, chestnut, apple, sugar maple, and hickory. A 

 straight glass tube, three feet in length, with a bore about one 

 quarter of an inch in diameter, was joined by a conical rubber 

 connector with each of the detached roots, and the roots again 

 covered with the earth in which they grew. The tubes were 

 now fastened in a vertical position to stakes set near the ends 

 of the detached roots, which were one inch in diameter. They 

 were then filled with water to a certain point, which was care- 

 fully marked, and the changes occurring noted every day. 

 Sometimes the water in a tube would sink away, showing an 

 absorption of the fluid by the roots ; and again it would rise 

 and flow over the top of the tube, demonstrating the fact that 

 the absorbing power of the root was, sometimes at least, in 

 excess of the affinity of the cellulose of the wood for water. 

 It was well established that the wood of the roots of trees is in 

 a condition in early spring to absorb with avidity the water 

 from the tubes, while later in the season many of them exude 

 water freely, so as to cause the tubes to overflow. The 

 amount of absorption was recorded in inches, the minus sign 

 being prefixed to the numbers, while the exudation was meas- 

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