476 Ox Galvanic Electricity. 
sels and texture of white wood, and we find it on the 
surface of the wood. But this is all I can venture to say. 
It is certain that the annual growth of the wood takes 
place chiefly in the external layers; but it is not probable 
that a single layer is formed annually, between the bark and 
the wood. This is proved by the radii which pass from 
one stratum to the other without the least interruption. I 
have examined branches of the preceding year almost daily, 
but I never found a line of separation in the wood before 
Easter. After this season, I perceived suddenly in the 
month of July, the line which separated, a new and thick 
layer. This observation proves that the Jayer is not 
formed so regularly as generally supposed. I am of opi- 
nion, that the line of separation is produced by a contrac- 
tion of the interior wood, a shrinking which renders the 
interior more compact, and which separates it a little from 
the external Jayer without detaching it entirely. We may 
therefore say, that every vear a new layer is formed, but the 
growth does not take place in layers. The growth does 
not differ from that of the monocotyledontal plants: it 
takes place wherever the parts are still soft and tender: a 
vessel is developed among the rest, as a cellule is formed 
among other cellules. All organized bodies increase in 
this manner: the development of new organs always takes 
place in the intervals of those which are already formed. 
I shal] treat in a subsequent memoir, of the growth and 
origin of the other parts of the plant. Ihave discovered 
many-things which strike me as being remarkable, but they 
require still further observation, 
LXXVII. On Galvanic Electricity. 
To Mr. Tilloch. 
Sir, Every admirer of chemical philosophy must have 
felt himself much interested, by the communication of Mr. 
Walker, in the last number of the Philosophical Magazine. 
T assure you that I was exceedingly so, and I hope it will 
not be thought, that in making the following observations, 
T at all detract from his praise.. They certainly corroborate 
his opinion. 
It is now seven or eight years since I attended Dr. Wol-- 
jJaston’s Chemical Lectures at Cambridge, but it will be im- 
possible for me ever to forget the last that I heard oe de- 
iver, 
