PHENOMENA OF PLANT-LIFE. 55 



and the wood of the vine was a hindrance to the sudden 

 upward thrust of the sap. After the foliage was developed, 

 the suction was limited to from -^6 to -12 feet of water, on 

 account, doubtless, of tire porous character of the foliage and 

 young branches, and there was no great difference between 

 the gauges. 



The flow of- sap from the sugar maple, so familiar to all, 

 and yet so variable and peculiar, was the first object of inves- 

 tigation in the beginning of these experiments, in 1873, but 

 its mysterious fluctuations were not fully known nor under- 

 stood until the close of the year 1874. The extraordinary 

 fac^s, that the flow occurred in mid-winter and early spring, 

 when the ground was covered with snow and there were no 

 signs of life ; that the flow began only during mild days 

 immediately following a severe frost, and ceased usually after 

 a few hours ; that when a cavity was cut into a sugar maple 

 tree, the sap flowed down from above, while in a birch it 

 flowed most freely from below ; and especially the fact, that 

 when a gauge was attached to a tree, it exhibited the most 

 surprising variations from great pressure, during the day, to 

 powerful suction at night, these, and other unaccountable 

 things, seemed to demand special effort to discover all the 

 phenomena attending the flow of maple sap ; and then, if 

 possible, to invent some rational explanation of them. 



Accordingly, a large number of experiments were devised 

 and carried out, with a very great amount of labor and no little 

 expense. Among them were the collection and weighing of 

 all the sap which would flow from a healthy tree, from Novem- 

 ber to the following May, with a careful observation of the 

 times when the flow began and ceased, in each case of good 

 sap-weather ; the collection, weighing and analysis of sap dur- 

 ing different periods of the entire season, both from the usual 

 level and from the top of a tree thirty feet from the ground ; 

 the collection and examination of the gas which escapes with 

 the first flow of sap from the orifice first made m a tree in the 

 spring ; the effect of increasing the number of holes upon the 

 total flow of sap and the entire product of sugar ; the result 

 of tapping trees at various elevations from the earth, on 

 different sides, and to different depths ; and finally, a record 

 for comparison and study of the fluctuations in the mercury 



