222 
affected it $ particularly the laurel and the laurus- 
tinus. 
It will be proper to mention the facts which 
show, that in many cases fluids descend through 
the bark. Mr. Knight has shown, in the Philo- 
sophical Transactions, that long strips of bark, 
every where detached from the alburnum of the 
tree, except at their upper ends, deposited as 
much alburnum as they could have done, if they 
had retained their natural position. In these 
cases, the sap must have descended through the 
bark wholly. 
M. Baisse placed branches of different trees in 
an infusion of madder, and kept them there for a 
long time. He found, in all cases, that the wood 
became red before the bark ; and that the bark 
began to receive no tinge till the whole of the 
wood was coloured, and till the leaves were af- 
fected ; and that the colouring matter first appeared 
above, in the bark immediately in contact with the 
leaves. 
Similar experiments were made by M. Bonnet, 
and with analogous results, though not so perfectly 
distinct as those of M. Baisse. 
Du Hamel found, that in different species of 
the pine and other trees, when strips of bark were 
removed, the upper part of the wound only emitted 
fluid, whilst the lower part remained dry. 
This may likewise be observed in the summer in 
fruit trees, when the bark is wounded, the alburnum 
remaining untouched. 
The motion of the sap through the bark seems 
principally to depend upon gravitation. When the 
