Dr. Bell on the Phyfiology of Plants, 417 



till at laft, it reached the highefl:. 2. If, in the 

 beginning of the bleeding feafon, before the fap 

 is found in the ftenn or branches, an incifion be 

 made in the root of a vine, a confiderable flow 

 of fap will follow the wound. 3. The quan- 

 tity of fap is very generally proportioned to the 

 humidity of the foil.* 



II. Of the courfe of the succus proprius. 



When a portion of the bark and wood of 

 the pine, is cut from the ftem, ihcjuccus proprius 

 flows in confiderable quantity both from the 

 upper and under margin of the incifion. Hence 

 it occurred to botanifts, that this juice might 

 have little or no motion, and that its efflux from 

 fuch an orifice might depend entirely on its 

 being freed from the preflTure of the bark and 



* It may fWl be a/ked. Why the fap flows mod from 

 the fuperior margin of each incifion, fuppofing it to arife 

 from the roots ? The incifion, it is faid, hurts or deftroys 

 the energy of the fxp-veffels for a confiderable way below, 

 whence the fap is not propelled upwards, againft its own 

 weight, and the pre/fure of the atmofphere now admitted. 

 From the divided vefTels, it pafies by a lateral communii 

 cation (for there are fap-vefi-els in every dircaion) into 

 thofe undivided, and when it has got above the incifion. 

 it again paffes laterally into the divided veffels; and falli 

 ing downwards, from its own gravity, a want of continuity 

 of veffels, and the diminiflicd preflure of the atmofphere, 

 it flows from the fuperior margin of the incifion. J, C, 



Vol. II. E e wood. 



