k 



I 



\ 



UMBILICAL VESSELS 



Sect. III. II. 8 



buds, which begin to enlarge as foon as they are formed, and in th 

 clinnate have their progrefs flopped by the cold during the winte 

 and the moifture which exfudes from the fides of thefe velTels, ar 

 IS extravafated between the alburnum and the bark, cai 

 leparation of them from each other. 



fes 



id 



From the new flow of fap in thefe veffels about midfummer, bein 



t> 



probably in part conveyed to th 



by the rotrograde action 



f 



th 



lymphatics in very hot weather, the honey-dew feems 



ginate either as an exfudation from the leaf, or from the veflels be 



1 



& 



pun6lured by the aphis, which drinks the vegetable chyle in fuch 

 great quantity that it pafTes through the infed almoft unchanged ; 

 fee Se6l. XIV. i. 7. and 3. 2 ; and thus caufes the fufFufion of honey 

 on the leaves below them for a time in the heat of fummer. 



Add to this that M. Du Hamel, by nicely meafuring fome buds, 

 found that they were gradually enlarged at fome times during the 

 winter, and concludes from thence that the fap-juice, which nourifhes 

 them, continues to flow, though flowly, in the milder parts of the 

 winter days. Vol. II. p. 262 ; and adds, that it muft rife continually 

 during the winter months in ever-green trees, otherwife their fo- 

 liage would wither ; and alfo in deciduous trees, becaufe the branch 

 of an ever-green tree will grow on a deciduous tree, and not lofe its 

 leaves in the winter, as the lauro-cerafus on a cherry-tree, and an 



F 



ever-green oak on a common oak. 



It muft neverthelefs beobferved, that as the umbilical veflels are a 

 part of the new bud, as the latfleals and other abforbents are a part of 



/ 



th 



hick or fetus, the perpetual a6l 



f thefe umbilical veflels 



jTJufl: depend on the bud to which they belong, in the caudex of which 



between the plumula and rad 



th 



e 



brai 



common fenforium 



4 



and the confequent vital energy, are believed to refide ; and, that whe 

 ther an ingraftment exifts between the bud and the umbilical ab 



forbent veflfel 



not. 



But as in thofe animals which have a very 



fmall 



