SAP in TREES. 9 



OBS. 3. When the birch is in a bleeding ftate, no fap iflues 

 upon incilion, till the knife has penetrated through the bark. 

 The fap then appears in fuch plenty, between wood and bark, 

 as to run ; and runs (till more plentifully if the incifion paffes 

 into the wood. But not a drop of fap can be made to ifTue 

 from the bark, whatever way it is cut. 



OBS. 4. It appears, that, in the beginning of the bleeding feafon, 

 when the thermometer, at noon, is about 49. or between 46. 

 and 50. and at midnight about 42. or between 40. and 44. 

 that the fap rifes about one foot in twenty-four hours, in the 

 trunk of the birch, if not formerly raifed by a greater heat. 



BY other trials, it was found, that, in the fame feafon, when the 

 thermometer, at mid-day, is about 45. and, at midnight, 

 about 38. the fap then afcends only about one foot in two days ; 

 and that it does not afcend at all unlefs the mid-day heat is 

 above 40. 



MARCH 13. 



THE incifion one foot high bled ; but the incilion two feet 

 high, and all above it, were dry. 



Thermometer, at noon, 44. ; at midnight, 42. 

 OBS. 5. It is here obfervable, that the incifion two feet high was 

 this day dry, although it had bled the day before. The caufe 

 is obvious from the thermometer. The cold of 41. during 

 the preceding night, had bound up the fap ; and the heat of 

 44. during the day, was not able to make it bleed at the height 

 to which it had been advanced by the heat of 49. on the pre- 

 ceding day. 



MARCH 14. 



Thermometer, at noon, 48. ; at midnight, 45. 

 THIS day the fourth incifion, at the height of. three feet, be- 

 gan to bleed ; the fifth was moift, but all above it were dry as 

 formerly. 



B OBS. 6. 



