VESSELS. , i 



cur chiefly in the stems of herbaceous plants, in young 

 shoots of tree3 and shrubs, and in leaves of every 

 description. They have rarely been detected either 

 in the mature wood or in the root, and the stems and 

 leaf-stalks of Liliaceous vegetables exhibit them to the 

 best advantage.* Of the nature and uses of these ves- 

 sels, but little is known. Some have described them 

 as the tubes through which the sap is propelled. Oth- 

 ers as air vessels which accompany the tubes through 

 which the sap passes in its ascent towards the leaf. 

 We know that healthy vegetation requires the pres- 

 ence of atmospheric air and it is reasonable to suppose, 

 that like the other substances by which plants are nour- 

 ished, this is furnished with an appropriate system of 

 vessels, and surely nothing could be better calculated 

 to answer this intention, than the spiral tubes which 

 we have seen in the leaves and their appendages. 



4. False Spiral Tubes— Fig. 4 c. These appear 

 somewhat intermediate between the two preceding, 

 having transverse fissures, analagous to the pores of 

 the one and between these fissures rings which are not 

 unlike the spiral coat of the other. They occur more 

 frequently in herbaceous plants, and are particularly 

 abundant in the soft texture of the Vine, and it is proba- 

 ble that they are formed by the partial union of the 

 Spiral rings. This idea has been confirmed by inspect- 

 ing the Flowering Rush in which they are of a mixed 

 character the same vessel exhibiting the arrangement 

 of each variety being at once porous, spiral, and also in- 

 tersected by transverse fissures. Fig. 4 d. 



5. Small Tubes are the only ones which remain to be 



• No plants which I have examined, exhibit them so distinct- 

 ly, as the Skunk's Cabbage, which is well named and figured in 

 the American Medical Botany of Dr. Bigelow. 



