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Sect. III. II. 3 



UMBILICAL VESSELS 



^ 



I 



1 



Thefe umbilical veffels, which fupply the buds of plants wth nou- 

 (hment iu the eady fpring, and unfold their foliage have been much 

 attended to by Dr. Hales and Dr. Walker (Edmb Plul. Tranfaa 

 Vol. I.) The former obferved, that the fap from the flump ot - •— 



which he had cut ofF in the beginnm 



of April 



ty 



which he had cut otr in uie dc^uiuu,^ w. ..4...-, ^.- , 



feet high in glafs tubes affixed to it for that purpofe, but which 



few weeks ceafed to bleed 

 the afcending fap 



Dr.Walker alfo marked the progrefs of 

 branches of trees, and obferved, that in 



V 



cold weather it flopped many hours in a day, as well as in the night, 

 and found likewife as fodn as the leaves became expanded, that the 



r , 



wounded trees ceafed to bleed. 



The veflels, which convey the fap-juice with fuch amazing force,are 

 fituated in or compofe the alburnum, or fap-wood, of the trunk or root 

 of the tree; nor is it furprizing, that fome of it when preffed by fo 

 high a column (hould exfude into the cells between the alburnum 

 and bark, as in thefe cells much fap-juice was obferved by Dr..Walker, 

 and this accounts for the great eafe with which the barks of willows 

 and of oaks are fcparated in the fpring from their wood. The abforb- 

 ent mouths of thefe fap-veflels open externally in the moid earth on 

 the roots of trees, and alfo into the air on their trunks; and thus mix 

 the aqueous fluids, which they thus imbibe, with the faccharine and 



4 



mucilaginous materials depofited previoufly 



the alburnum of thefe 



3 



and trunks. 



This afcending fap-juice during the fpring feafon is in fomc 

 fo fweet, that it is ufed in making wine, as that of the birch- 

 tree in this country; and fugar is procured in fuch quantity from a 

 maple in Penfylvania, that from each tree five or fix pounds of good 

 fuc^ar have been made annually without deftroying it. Rufh, on Sugar 

 Maple. Phillips^ London. This fugar is depofited I believe in the 



trees, as in the manna-afti, and 

 diffolved in the fpring by the moifture, which is drank up by the 



fap-wood of the trunk and roots of 



bforbents from the earth and atmofphere, and forcibly carried 



E2 € 



pand 



\ 



