54 
REPORT ON BOTANY, MDCCCXLI : 
which seems, therefore, to be more concentrated in the leaves ; 
and the growth of trees, in point of thickness, only commences 
after the leaves are capable of fulfilling their functions : this 
has been proved by all the measurements which the author 
instituted. The influence of the leaves upon the increase of 
trunks, in point of thickness, exhibited itself, among others, 
most distinctly in the Italian poplar. On one of these trees 
being deprived of almost all its branches, in the month of 
March, the increase in thickness was proportionably slight 
during the months of June and July. The growth of a lime 
tree, on the other hand, in which the side branches, also those 
lower down on the trunk, as well above as beneath the point 
of measurement, had, for the greater part, been purposely left, 
was considerable, and increasing every year. An experiment 
was made with two equal sized oaks, situated under the same 
circumstances, all the lateral branches were taken from one 
and left in the other ; the result was, that the increase of 
thickness, in the tree which had not been pruned, was much 
more considerable than of the one which had been pruned. 
The trunks of Monocotyledons also increase in thickness 
according to the observations of the author. An Aletris 
frag vans had increased by 17| millimeters in thickness in five 
years, and a trunk of Dracaena draco, by 23J millimeters 
in the same period of time. These excellent observations 
confirm the theory which Thouars has advanced, respecting 
the increase of trees in thickness, which I have endeavoured 
to represent, at least in its principal features, in the elm. 
Phil, Bot. ed. 2, vol. i, p. 260, and in the Icon. Anat. Bot. 
part i. p. 7, fig. 10-12, 
In addition to the account formerly mentioned, of the dying 
of wood, and rendering it durable, by Br, Boucherie, we have 
now to add the Beport of the Commission of the Academy, 
consisting of Mirbel, Arago, Poncelet, Audouin, Combey, 
Boussingault, and Dumas (Compt, Bend. 1840, vol. ii. p. 894). 
It is not necessary, they say, that the tree should have 
all its branches and all its leaves, it is only requisite to 
leave a tuft at the point, in order to efiect the imbibition. It 
is not requisite that the tree should remain standing, it may 
446 
