50 OF THE SAP-VESSELS. 



periments and observations, to be hereafter enlarpjed up- 

 on, prove also that air exists in the vegetable body, and 

 must likewise l^e contained in appropriate vessels. Be- 

 sides these, we know that plants are nourisliedand invi- 

 gorated by water, which they readily absorb, and which 

 is quickly conveyed through their stalks and leaves, no 

 doubt by tubes or vessels on purpose. Finally, it is ob- 

 servable that all plants, as far as any experiment has 

 been made, contain a common fluid, which at certain 

 seasons of the year is to be obtained in great quantity, 

 as from vine branches by wounding them in the spring 

 before the leaves appear, and this is properly called the 

 sap. It is really the blood of the plant, by which its 

 whole body is nourished, and from which the peculiar 

 secretions are made. 



The great difficulty has been to ascertain the vessels 

 in which the sap runs. Two of the most distinguished 

 inquirers into the subject, Malpighi and Grew, believed 

 the^woody fibres, which make so large a part oi the 

 vegetable body, and give it consistence and strength, to 

 be the sap-vessels, analogous to the blood-vessels of 

 animals, and their opinion was adopted by Du Hamel. 

 In support of this theory it was justly observed that these 

 fibres are very numerous and strong, running longitudi- 

 nally, often situated with great uniformit}' (an argument 

 for their great importance,) and found in all parts of a 

 plant, although in some they are so delicate as to be 

 scarcely discernible. But philosophers sought in vain 

 for any perforation, any thing like a tubular structure, 

 in the woody fibres to countenance this hypothesi^^, for 

 they are divisible almost without end, like the muscular 



