46 PHENOMENA OF PLANT-LIFE. 



sugar maple flows at any time when stripped of its foliage, 

 provided the weather is favorable, the principal condition 

 being a temperature above freezing, directly after severe 

 frost. A comparison of the flow from this species with the 

 pressure on the mercurial gauges, and with the temperature 

 as indicated in the meteorological observations, kindly furn- 

 ished by Prof. E. S. Snell, LL.D., of Amherst College, will 

 convince the inquirer that there is an intimate connection 

 between these three sets of facts. 



The quantity of sap from a sugar maple during the season 

 is much greater than from any other tree flowing from the 

 same causes. Thus the entire flow from the butternut was 

 less than the product of the sugar maple for a single day. 

 The ironwood and the birches, however, surpass even the 

 maple, both in the rapidity and amount of their flowing, if we 

 make allowance for the difference in the size of the trees tested. 

 A paper birch, fifteen inches in diameter, flowed in less than 

 two months one thousand four hundred and eighty-six pounds 

 of sap ; the maximum flow, on the fifth of May, amounting 

 to sixty-three pounds and four ounces, which is probably 

 three times the average yield of a sugar maple of the same 

 size. These latter species will not bleed during the winter, 

 and seem to do so in the spring from a cause entirely difier- 

 ent from that which affects the trees which bleed in fall and 

 winter. The grape, which is often thought to bleed more 

 freely than any other species, though later in the season, really 

 flows but little, the total amount from a very large vine being 

 eleven pounds and nine ounces. 



Among the species subjected to trial, only those mentioned 

 as bleeding exhibited this phenomenon. The following flowed 

 for a short time, or very irregularly, or very slowly. The 

 shad-bush was seen to flow, on the eighth of April, one drop 

 in fifty seconds. The hickory bled one drop per minute of 

 very sweet sap, on the fifteenth of April, and the cornel, ten 

 drops on the same day. The European alder flowed three 

 drops per minute, April ninth, and the common alder, four 

 drops, on the twenty-first of March, and on the tenth of April, 

 nine drops from one spout and six drops from another, in- 

 serted six inches below the former. The black walnut yielded 

 a small amount of sap during several weeks, and, March 



