WOOD AND BARK OF TREE£. 
87 
cases where the contrary has happened, I conceive the presence mini shed 
of too much moisture, and the consequent oxydation of the zinc * wt ' vo 
surfaces must have been the deteriorating cause. 
Prince's Street, May 10, 1813. 
III. 
On the Wood and Bark of Trees much magnified. By Mrs . 
Agnes Jbeetson. 
To Mr. Nicholson. 
SIR, 
I T was my intention that this letter should have concluded 
all I had to recount on the roots of fruit trees, and also of 
the same part in those plants which rise yearly from the earth ; 
but I find it impossible, (let my study of the subject have been 
ever so perfect,) to write properly on it, without having the 
object before me. This, though it makes my labour excessive, 
also, I hope, makes it more exact. The necessity of review- 
ing every part as often as I write on it, has made me correct 
many,a fault, and destroy many an error, that would otherwise 
have appeared in my phytological review ; but it will also im- 
pede my giving the subject I intended, in lieu of luhich I shall 
produce an exact delineation of wood, extremely magnified, both delineate 
: , , . , . . , ' “ . , the wood 
in the root and m the stem j pointing out the variation to be muc h magni- 
found in the two ; the form of the sap vessels j the construe- f ie d* 
tion of the bastard vessels ; the management of the silver 
grain j and shew also how the net is contrived in which the 
sap vessels are inserted, and many circumstances that will draw 
their sources from this subject ; and conclude my letter with 
dissections of the formation of the bark ; shewing how impossi- 
ble it is thaUhat part can possess any returning sap vessels ; 
since, except those of the inner bark, (which their thick liquid 
so exactly identifies,) all the vessels run in a contrary direction. 
I 
