64 ON CAMBIUM. 



CONVERSATION VI. 



ON CAMBIUM, AND THE PECULIAR JUICES OF PLANTS. 



Mrs. B. Having traced the sap in its ascent to the 

 extremity of the leaves, and converted it, by the changes 

 it undergoes in that chemical laboratory, into an homo- 

 geneous liquid adapted to the nourishment of the plant ; 

 we must now, following it in its descent, observe in what 

 manner it performs this office. 



The sap, thus changed, assumes the name of Cambium 

 or returning sap, and passes into another system of ves- 

 sels which convey it downwards, chiefly through the liber, 

 or most internal layer of bark, and a small portion through 

 the alburnum, or young wood ; and, as it traverses the 

 several organs, it deposits in each the various matters re- 

 quisite for their sustenance. 



Caroline. Having compared the ascending sap to chyle, 

 Mrs. B., we may find a still greater analogy between the 

 cambium and blood, into which chyle is converted, after 

 having passed through the heart and lungs, and been ren- 

 dered fit to nourish the animal frame. 



Mrs. B. We have already observed, that the chemical 

 changes which take place in the leaves, in order to con- 

 vert the sap into cambium, are in many respects analogous 

 to those which take place in the heart and lungs, in order 

 to convert the chyle into blood. 



Emily. True : in both cases the atmosphere is the 

 agent ; with this difference, however, that it carries off 

 carbon from the animal system, while it is the means of 

 accumulating carbon in that of vegetables. 



Caroline. But if the cambium descends through the 

 liber, how does it find its way in endogenous plants, 

 which have no bark ? 



Mrs. B. Its passage in monocotyledons has not been 

 well ascertained. It is probable, that the fibres of the 



457. By what name is the sap called when it descends'? 458. 

 Through what parts of the plant does it descend 1 459. What has al- 

 ready been remarked of the chemical changes which take place in sapl 

 460. Is it known through what portion of the monocotyledons sap de- 

 scends'? 



