« TIME OF FLOWING. 183 



those of the followmg genera showed any tendency to bleed, 

 viz. : Betula, which includes the birches ; Acer, the maplesj 

 Vitis, the vines ; Ostrya, the hornbeam ; Juglans, the wal- 

 nuts. The genus Carya, to which belong the hickories, 

 sometimes exudes a very little sap, and possibly the Fagus 

 or beech, and Carpinus, the hop hornbeam, may do the same, 

 though no opportunity offered for testing them satisfactorily. 

 ,0u the 19th of March, when the ground was still covered 

 with snow, but free from frost, fourteen species of the com- 

 mon forest-trees were tapped, and nearly all the species 

 brought under observation were tapped, first on the 21st of 

 April, and again on the 30th of the same month. 



It Avas discovered that each species of those which flowed 

 had its own time of beginning, when it seemed to awake 

 from its winter's repose ; that the flow steadily increased in 

 quantity and force, as indicated by the weight of sap and the 

 pressure on a mercurial gauge, until it reached its maximum, 

 and then gradually declined ; and that the composition of the 

 sap of the several species differed remarkably, according to 

 the date of the flow and especially the time of its beginning. 



This singular periodicity, peculiar to ever}'" species, demon- 

 strates that the absorption of water by the rootlets is not 

 caused by osmose, or any other mere physical force, but is 

 the result of the specific life, which imparts to every plant its 

 distinctive characteristics. 



The sugar-maple begins to flow in October, reaches its 

 maximum about the first of April, and ceases about the first 

 of May.* The black birch begins to flow the last of March, 

 attains its maximum the last of April, and stops about the 

 middle of May. The wild summer grape-vine commences 

 about the first of May, arrives at its maximum of flow and 

 pressure about the 20th of May, and ceases early in June. 



This difference in the season of flowing is, of course, 

 accompanied by a corresponding variation in the temperature 

 of the soil and the atmosphere, and very naturally also in the 

 chemical composition of the sap. Thus the principal ingre- 



* Mr. H. S. Go.odale, of Mount Washington, Mass., a membei' of the Board of 

 Agriculture, states that he has made maple-sugar from sap collected in the months of 

 October, November, January, February, March, April and May. 



