VEGETABLE SAP. 119 



that its specific qualities are acquired from the pre- 

 existing- essentials of the plant, and from the elabo- 

 rating- powers of the organic structure under the 

 action of air, light, and heat ; that, whether as liquid 

 or as vapour, its motion, generated by heat, must 

 necessarily be upwards, if not impelled or attracted in 

 any other direction. Whether it be capable of sink- 

 ing- by its own weig-ht is, perhaps, questionable ; 

 because there must be a vacuum somewhere to 

 receive it, or it must displace some other fluid which 

 must ascend out of its way, and the tubes containing 

 it being all sealed at the top, prevent the perpendi- 

 cular pressure of the atmosphere ; and though true, 

 that when abundant and fluid, it distils from the upper 

 side of a wound as well as from the lower, yet it con- 

 tinues to ooze away from below longer than it flows 

 from above, whether the wound be made in the 

 spring or in the autumn. Example, a felled tree: 

 while the dissevered butt of the stem is quickly 

 dried, the root remaining in the ground, will continue 

 to bleed for months after jthe separation. The sap, 

 therefore, besides its direct motion, is capable of being- 

 diffused through the whole body of cellular and vas- 

 cular matter, and of course flows towards any outlet? 

 whether that be aspiring shoots, perspiring foliage, 

 swelling fruit, empty vessels, or bleeding wounds*. 



* A curious instance of the counter currents of some component 

 of the sap is observahle in the common aquatic plant Chara* 

 Bright globules are seen to rise and fall in the vessels, exactly simi- 

 lar to what is seen in fermenting liquors. 



