278 FAttTS OF TREES FIRST IMPAIRED BY AGE. 



made by canker, have been wholly covered with new and 



showe<l, that healthy bark. These facts, therefore, satisfied me, that the 



there was no debility and disease* of old varieties of fruits of this species 



deftctiveac- ,j . . . 



tion of th-? did not originate in any defective action of the bark or 



bark oralbur- albiirnnm, either of the root, or of the stem and branches, 

 and my attention was consequently directed to the leaf and 

 succulent annual shoot. 

 Experiments ^ ^^^ crab-stocks were grafted with cuttings of the gol- 

 on the leaves den pippin, in a situation and soil, where 1 had previously 

 shoots, ascertained, that the wood of the goldin pippin rarely re- 



mained 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, whicii had recently sprung from seed, were in- 

 serted m 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 ih!^ 

 leaves of these Lad unfolded, and entered on their oifice,' 

 every symptom of debility and disease disappeared in the 

 bark and wood of the goldeti pippin: and each conti- 

 nued to perform its office, just as well as the wood -and 

 bark of tbe young needling stocks ^ould have done- under 

 similar circumstances. 1 made nearly the same experi- 

 ments on the pear tree, and with the same result. 

 Thesapclrcur I have endeavoured, in several former communications, to 



lates through p^^^-^ ^^^^ the sap of plants circulates throui^h their leaves, 



the leaves, as " * ... 



the blood as the blood of animals circulates through their lungs; and 



lun^^s^'^ ^^^ ^ ^^^^ ^^^ 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 

 trees, of old and debilitated varieties of fruit, became most 

 diseased in rich soils, and when grafted on stocks of the 

 most vigorous growth ; which has mduced me to suspect, 

 tliat in such cases more food is collected, and carried up 

 into the plant, than its leaves can prepare and assimilate, 

 and that the matter thus collected, which would have pro- 

 moted the health and growth in a vigorous variety, accn- 

 mulaites, and generates disease in the extremities of the 

 branches and annual shoots, while the lower part of the 

 frunk and roots remain, generally, free from any apparent 



disease. 



