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44 



PULMONARY ARTERIES 



Sect. IV. 1. 4, 



All thefe appearances were more eafily feen in a leaf of picris treated 



lie manner ; for in this milky plant the ftems and middle- 



the fa 



rib of the leaves are fornetimes naturally coloured reddiOi, and henc 

 the colour of the madder feemed to pafs further into the ramification 

 of their leaf-arteries, and was there beautifully vifible with the re 

 turning branches of milky veins on each fide. 



In a plant which was fent to me under the name of fenecio bicoloi 



but which I have not yet feen 



flow 



th 



pper furface of th 



leaf is green like moft other leaves, but during the vernal months 

 the under furface is of a deep red, whence I conclude that the vege- 

 table blood acquires the red colour in the terminations of the pulmo- 



;r furfaces of the leaves, which becomes vifible 



nary artery in the upp 

 as it paffes in th 



on 



th 



e 



ferior furfac 



In the fame 



manner the red colour of the blood is moft vifible in the larg 



beneath the leaf of the red veined dock, rumex fanguinea. 



4. From thefe experiments the upper furface of the leaf appealed to 

 be the immediate organ of refpiration, becaufe the coloured fluid was 



carried to the extremities of the leaf by velTels mofl: confpicuous 

 the upper furface, and there changed into a milky fluid, which 



on 



the blood of th 



plan 



and then returned by concomitant 



the under furface, which were feen to ooze when divided with fcif- 

 fars, and which in picris particularly rendered the under furface of 

 the leaves greatly whiter than the upper 



As the upper furface of leaves conftitutes the organ of refpiration, 

 on which the vegetable blood is expofed in the terminations of arteries 

 beneath athin moift pellicle to theaaion of the atmofphere, thefe furfaces 

 in many plants ftrongly repel moifture, as cabbage-leaves, whence the 

 particles of rain lying over their furfaces without touching them, as 

 obferved by Mr. Melville, (ElTays Literary and Philof. Edinb.) h 



th 



ppearance of globules of quick-fil 



And h 



leaves laid 



with their upper furfaces on water wither as foon as in the dry 



but continue green many days if placed with their upder furfaces 



water 





I 



