434 PROCEEDINGS OF THE BRITISH ASSOCIATION. 



3. The bark and two layers of alburnum were cut away. The tree was at the 

 time unhealthy ; it, however, put forth its leaves on that and the ensuing spring, 

 but shortly after died. No sap was observed above or below the wounded part. 

 Roots were developed from the upper, and branches from the lower part of the 

 section. 



4. The bark and six layers of alburnum were taken off. The tree became 

 much less vigorous, but did not die, and otherwise presented the same appear- 

 ance as the last. 



5. The bark and twelve layers of alburnum were stripped. The consequences 

 were again similar to the last two ; the alburnum above and below the cut being 

 dry, but an accidental cut that penetrated into the heart-wood exuded sap. 



6. This was a repetition of the experiment of Palisot de Beauvais, but on a 

 much larger scale, by cutting away a circular ring of bark around a single branch. 

 The branch continued to grow, and roots sprouted from the under surface of the 

 isolated bark and branch. 



7. In this the whole of the wood of the tree was cut away, except four pillars, 

 composed of bark and sap-wood. In this case the sap first appeared from above, 

 descending by the pith, and then from the heart-wood, the alburnum being dry. 

 In this case the sap must have passed up the alburnum, and horizontally through 

 to the heart- wood. 



Mr. Nevan inferred from these experiments — 1. That the life of the tree does 

 not depend on the liber or cambium. 2. A descent of sap takes place before the 

 development of leaves. 3. That new matter arises from below ; which had not 

 previously been allowed. He thought there were two distinct principles in the 

 tree, — one the ascending, or leaf-principle; the other the descending, or root 

 principle. Mr. Nevan had also performed some experiments on the conversion 

 of roots into branches, and came to the conclusion that buds or branches might 

 be developed from any part of the root above its extreme end, from which point 

 it was impossible for buds to be developed. 



Professor Lindley remarked that these experiments confirmed entirely the 

 theory of the structure of wood adopted by Du Petit Thouars. He did not 

 think that the existence of any new principle could be inferred from the experi- 

 ments. In the seventh experiment the horizontal circulation of the sap was 

 proved, which confirmed the accuracy of Hale's experiment, in which he cut a 

 tree on alternate sides, almost through, and found the sap still ascended perfectly 

 well. With regard to buds proceeding from roots, their occasional formation on 

 these parts had long been well known, and they might always be certainly 

 developed where the roots assumed the situation or character of the stem. He 

 then alluded to a plant lately brought to Europe (Cissus hydrophora) in which 

 the fibres of wood, as they descended from the leaves, separated in the form of 



