22 PHENOMENA OF VEGETATION. 



But this experiment has not satisfied all others. First of all, the 

 branch thus treated died in three days ; and then, even if it had lived 

 longer, it might have been said that the vegetable cut off from the 

 nourishing sap may have been able to absorb more than its usual 

 ration of clear water. It was in the situation of an animal deprived 

 of substantial aliment, which availed itself of pots of weak bouillon, 

 and yet died of hunger. And, moreover, the experiment has been 

 repeated not with a branch but with a young tree deprived of its 

 roots, and the evaporation proved to be very insignificant." 



But whatever may be said of such experiments, and of calculations 

 founded on them, we have other means of testing the quantities of 

 water passing through trees in the process of their growth ; and we 

 find they must be far from inconsiderable. I have cited one state- 

 ment by Marsh, with this I cite also the following : — 



"The amount of sap which can be withdrawn from living trees 

 furnishes, not, indeed, a measure of the quantity of water sucked up 

 by the roots from the ground — for we cannot extract from a ti-ee its 

 whole moisture — but it supplies numerical data which may aid the 

 imagination to form a genei-al notion of the powerful action of the 

 forest as an absorbent of humidity from the earth. 



" The only forest tree, known to Europe and North America, the 

 sap of which is largely enough applied to economical uses to have 

 made the amount of its flow a matter of practical importance and 

 popular observation, is the sugar maple, -4cer saccharinum of Anglo- 

 American Provinces and States. In the course of a single * sugar 

 season,' which lasts ordinarily from twenty-five to thirty days, a sugar 

 maple, two feet in diameter, will yield not less than twenty gallons of 

 sap, and sometimes much more. This, however, is but a trifling 

 proportion of the water abstracted from the earth by the roots during 

 this season ; for all the fluid runs from two or three incisions or 

 augur holes, so narrow as to intercept the current of circulation of 

 comparatively few of the sap vessels, and, besides, experience shows 

 that large as is the quantity withdrawn from the circulation, it is 

 relatively too small to afi'ect very sensibly the growth of the tree. 

 The number of large maple trees on an acre is frequently not less than 

 fifty, and, of course, the quantity of moisture abstracted from the soil 

 is measured by thousands of gallons to the acre. The sugar orchards, 

 as they are called, contain also many young maples too small for 

 tapping, and numerous other trees — two of which, at least, the Black 

 Birch, Betula lenta, and Yellow Birch, Betula exeelsa, both very 

 common in the same climate and far more abundant in sap than the 



