184 Account of the American Sugar Maple. 



in Dr. Tongue's opinion, who fuppofes that changes in the 

 weather of every kind might be as readily afcertained by 

 difcharges of fap from trees, as by the barometer. (Vide 

 Philofophical Tranfactions, N° 68.) Warm days fucceeding 

 frofty nights are moft favourable to a plentiful difcharge of 

 fap. If frofly nights fucceed a warm day, there is always a 

 total fufpenlion of the difcharge*. 



The 



* Dr. Hale, in his Vegetable Statics, relates that he cut down a vine, and 

 cemented to its mutilated (lump glafs tubes, each 7 feet long, and one 

 fourth of an inch diameter, with brafs caps, by which they were fcrewed 

 on one above another, till they rofe to the height of 36 feet. 



By thefe gages it appeared, 5 



ift. That the fap began to rife March 10, when the thermometer by 

 day flood only at 3 degrees above the freezing point. 



adly. Thar, April 18, it was at its height and vigour. 



3dly. That from that time to May 5, the force gradually decreafed. 



4thly. That it conllantly rofe fafteft from fun-rife to about 9 or 10 in 

 the morning, and then gradually fubfidcd till about 5 or 6 o'clock in the 

 afternoon. 



5thly. That it rofe fooner in the morning after cool weather, than after 

 hot days, and in proportion to die coldnefs of the night and fubfequent 

 hear. 



<ithly, Tliat after feveval fucceffive cold days and nights, the fap would 

 fife during the whole day, if it chanced to be fine, although flowed at noon. 



7thly. That if warm weather had made the fap flow vigorously, that 

 vigour would be abated immediately by a cold eafterly wind and a cloudy 

 fun, when the fap would fink at the rate of an inch per minute ; but when 

 the fun flione out, and the wind fluffed, it rofe again as ufual. 



Sthly. The oldeft vines were fooneft affected by a change of tempera- 

 ture, and in them the fap firft began to fink. 



Othly. And, on the contrary, when the tube was fixed to a very fhort 

 flump of a young vine, and at only 7 inches from the ground, the fap 

 flowed jnceffantly, and fafteft of all, in thegreateft heat of the day, finking 

 only after fun-fet. 



He then makes this general conclufion, that the rapidity with which the 

 fap circulates in the vine during the fpring, is five times greater than the 

 rapidity with which the blood flows in the arteries of a horfe; that it is 

 confiderably flower in the fummer than in fpring, very languid in autumn, 

 and ceafes altogether in the winter. 



The 



