primarily impaired by Age . 181 
the wounds, previously made by canker, have been wholly 
covered with new and healthy bark. These facts, therefore, 
satisfied me, that the debility and diseases of old varieties of 
fruit of this species, did not originate in any defective action 
of the bark or alburnum, either of the root, or of the stem 
and branches, and my attention was consequently directed to 
the leaf and succulent animal shoot. 
A few crab-stocks were grafted with cuttings of the golden 
pippin, in a situation and soil, where I had previously ascer- 
tained that the wood of the golden pippin rarely remained in 
health at the end of a second year ; and, as soon as the 
annual shoots had acquired sufficient growth and firmness, 
numerous buds of a new and luxuriant variety of apple, 
which had recently sprung from seed, were inserted in them. 
During the succeeding winter, the natural buds of the golden 
pippin branches were destroyed, and those inserted suffered 
alone to remain ; and as soon as the leaves of these had 
unfolded, and entered on their office, every symptom of 
debility and disease disappeared in the bark and wood of the 
golden pippin ; and each continued to perform its office, just 
as well as the wood and bark of the young seedling stocks 
could have done under similar circumstances. I made nearly 
the same experiments on the pear tree, and with the same 
result. 
I have endeavoured, in several former communications, to 
prove that the sap of plants circulates through their leaves, 
s the blood of animals circulates through their lungs ; and I 
have not subsequently found any facts, in the writings of 
other naturalists, or in my own experiments, which militate 
against this conclusion. I have also observed, that grafted 
MDCCCX. B h 
