British Association for the Advancement of Science. 291 
2. The bark and cambium were removed in the same manner. 
In August, 1837, this tree sickened, and there was no formation of 
wood or bark in the wounded part. Two developments, however, 
took place, one above the other, from below; the former having 
the appearance of roots, the latter were branches with leaves. 2 
_ 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 pre- 
sitted the same appearance 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 pene- 
trated into the heart-wood exuded sap. 
6. This was a repetition of the experiment of Palisot de Beau- 
vais, 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, ex- 
cept 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 taggers geen 
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 prin- 
ciple. 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 reniitieed that these experiments confirmed en- 
tirely the theory of the structure of wood adopted by Du Petit 
