a* On the MO 710 N of 



ing fap, we find it will run out in any direction, either up- 

 wards or downwards, wherever an incifion is made. 



MARCH 29. 



Thermometer, at noon, 46. ; at midnight, 42. 

 THE eighth incifion bled ; but the ninth was ftill dry. The 



inverted branch bled ftill freely at E. The feven incifions on 



the branch B did not bleed. 



OBS. 24. Dr TONGE *, in the laft century, firft noticed what he 

 termed the recidhation of the fap, that is, its fubfidence or 

 defcent in a tree during the cold of the night. This opinion 

 was alfo adopted by Dr HALES f, who fays, " That the fap 

 " in all vegetables does probably recede, in fome meafure, 

 " from the tops of branches, as the fun leaves them." It is 

 an opinion that has fince been generally admitted, and the 

 phenomenon itfelf termed the ocillatory motion of the fap. 



SUCH a motion of the fap, however, appeared very queftion- 

 able, on feveral occafions, in the courfe'of our prefent expe- 

 riment. Often, when the fap was rifen to a confiderable 

 height in the tree, the incifions which had formerly bled 

 would be found dry in a cold morning j but a warm gleam 

 of the fun would, of a fudden, fet them a-bleeding, not 

 fucceflively, but all at once. This feems to prove, that the 

 fap does not defcend when the incifions ceafe to bleed by an 

 increafe of cold, but is only bound up. 

 To verify or invalidate this conclufion, the following experi- 



.ments were made : 



EXP, 10. March 28. A luxuriant young birch, two inches in 

 diameter, was this day cut over, a foot above ground. Be- 

 ing cut at mid-day, both fedlions bled for two hours j but 

 the under one more plentifully than the other. The upper 

 fection became quite dry on the approach of night. The 



tree 



* Philof. Tranf. anno 1668. p. 855. 

 f HALES Staticks, vol. i. p. 145. 



