152 Vegetable Static}.** 



the attraction of the fuperior leaves, by the 

 bark placed N°. 12. but alfo without any 

 leaf-bud of its own, whofe branching fip-- 

 veffels, being like thofe of other leaf-buds 

 rooted downwards in the wood, might 

 thence draw fap, for the nourifhment of it- 

 felf and the adjoining bark, N°. 13. But 

 had thefe rooting fap veffels run upwards, 

 inflead of downwards, 'tis probable, that in 

 that cafe the upper part of each ringlet of 

 bark, and not the lower, would have fwel- 

 led, by having nourifhment thereby brought 

 to it from the inmoft wood. 



We may hence alfo fee the reafon why, 

 when a tree is unfruitful, it is brought to 

 bear fruit, by the taking ringlets of bark off 

 from its branches; viz. becaufe thereby a 

 lefs quantity of fap arifing, it is better di- 

 gefted and prepared for the nourifhment of 

 the fruit ; which from the greater quantity 

 of oil, that is ufually found in the feeds, 

 and their containing veffels, than in other 

 parts of plants, fhews that more fulphur and 

 air is requifite for their production, than 

 there is for the production of wood and 

 leaves. 



But the moft confiderable objection 

 againft this progreffive mo^on of the fap, 



without 



