STEMS, LEAVES, AND BUDS. 
55 
be cut down, after having previously taken away all its useless 
boughs, and must then be placed with its lower end immersed 
in the fluid which is intended to be absorbed. If it should not 
be desirable to cut down the tree, it is only necessary to make 
a hole in the trunk below, or to make an incision with a saw, 
and then to bring the fluid in contact with it. The permeating 
of the stem is eftected in a few days without difiiculty or labour. 
In order to make the wood more durable and harder, pyro- 
lignite de fer should be made use of for imbibition. The pine- 
wood acid is brought into contact with iron shavings, the com- 
bination takes place even in the cold, and then contains much 
of creosot ; and the latter, as is well known, is a preservative 
of all organic substances. In order to prevent the warping of 
the wood, Boucherie uses chloride of lime, or the lye of the 
places in which salt is prepared. It has already been stated, 
that wood may be died by causing fluids to pass into the tissues 
of trees, which, by their chemical effect upon each other, pro- 
duce colours. 
M. Payen has read a treatise at the Academy of Sciences 
in Paris, on the Leaf-nerves of the Dicotyledons^ which 
has been criticised by De Mirbel ; the critique is contained 
in the Annales des Sciences Naturelles, 2d Ser. Botaniq., 
V. 14, p. 220, and in the Comptes Bendus, 1840, v. 2. The 
treatise is praised on account of its practical applications. 
The author first considers the origin of the nerves from the 
vascular bundles of the wood in the branch, and enumerates 
three different kinds of origin ; — 1st, The unitary, if they spring 
from one vascular bundle : 2d, The ternary, if three vascular 
bundles unite in order to form the leaf-nerves ; and, 3d, The 
circulary, if the vascular bundles meet from the whole circum- 
ference of the wood. The vascular convolutions frequently 
run through the petiole of the leaf to the leaf, without expe- 
riencing a change, but frequently each divides itself into three 
fibres, which then either enter into the leaf on the same surface 
as the principal nerve, or on different surfaces. The simple 
leaf is produced, if the central vascular bundle separates itself 
from the wood at an earlier period than the two others ; if, 
however, the two lateral bundles liberate themselves first, then 
447 
