of the Organic Systems of Vegetables. 91 



sage the intercellular spaces, i. e., the unfilled interstices which 

 lie between the exterior parietes of contingent vessels. These 

 doctrines cannot all be true; they must be more fully examined 

 when we come to treat of the course of the sap and the assimi- 

 lation of their food by plants : but even now, when the re- 

 maining object is chiefly to distinguish by experiments the 

 respiration of plants from their digestion, and to follow out the 

 phenomena of the first-named process alone, even this cannot 

 be satisfactorily pursued without an enunciation of what expe- 

 riments hereafter to be detailed will more fully shew, viz. that 

 absorption takes place in most plants both by their roots and 

 leaves ; that the first course of the sap is upwards ; and that 

 its passage (at least its frequent passage) is through the non- 

 spiral tubes. Let one or two experiments illustrate these 

 points. 



During the last spring I had several notches cut in the 

 trunks of various trees, viz. lime, birch, horse-chestnut, &c., 

 and at several heights in each tree, from one to six feet ; the 

 result of which was, that in every instance the sap was seen 

 distinctly exuding from the lowest side of the lowest section 

 first, and progressively rising to the others day by day : but I 

 have found that the chief current of sap is axial, for it will 

 traverse the whole extent of the trunk before it will enter any 

 of the branches, how near soever to the root they may be 

 situate d; and also that when it does enter the branches its 

 course is still axial with regard to them, i. e. 9 it will pass to the 

 end of the main branch before it enters its lateral ramifications. 

 This tendency will explain two interesting facts : viz., first, 

 why plants which have lost their leaders raise one of the 

 drooping lateral branches, as in the Norway fir, the larch, &c. 

 &c., to the erect position ; and secondly, why it is generally 

 (perhaps invariably) found that terminal buds are the largest 

 and finest, and are always the first developed ; and also why 

 the topmost branches are in leaf before the buds of the lower 

 branches are expanded. 



To obviate the objections which have frequently been raised 

 against an experiment somewhat similar to those above de- 

 tailed, but in which holes were bored in the trunks of trees 

 with an augur, and to which observations it was urged, that 



