OP THE SAP- VESSELS. 45 



stalks and leaves, no doubt by tubes or ves- 

 sels on purpose. Finally, it is observable that 

 all plants, as far as any experiment has been 

 made, contain a common fluid, which at cer- 

 tain 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 sub- 

 ject, Malpighi and Grew, believed the woody 

 fibres, which make so large a part of the ve- 

 getable body, and give it consistence and 

 strength, to be the sap- vessels, analogous to- 

 the blood-vessels of animals, and their opi- 

 nion was adopted by Du Hamel. In support 

 of this theory it was justly observed that these 

 fibres are very numerous and strong, running* 

 longitudinally, often situated with great uni- 

 formity (an argument for their great import- 

 ance), and found in all parts of a plant, al- 

 .tko-ugh in some they are so delicate as to be 



