This seems to be distinctly shown by the observ- 
ations and experiments of Mr. Knight. He has, 
in a number of instances, transferred the young 
scions and healthy shoots from old esteemed fruit- 
bearing trees to young seedlings. They flourished 
for two or three years ; but they soon became dis- 
eased and sickly, like their parent trees. 
It is from this cause that so many of the apples 
formerly celebrated for their taste and their uses 
in the manufacture of cyder are gradually deterior- 
ating, and many will soon disappear. The red 
streak, and the moil, so excellent in the beginning 
of the last century, are now in the extremest stage 
of their decay ; and however carefully they are 
ingrafted, they merely tend to multiply a sickly and 
exhausted variety. 
The trees possessing the firmest and the least 
porous heart-wood are the longest in duration. 
In general the quantity of charcoal afforded by 
woods, offers a tolerably accurate indication of their 
durability : those most abundant in charcoal and 
earthy matter are most permanent ; and those that 
contain the largest proportion of gaseous elements 
are the most destructible. 
Amongst our own trees, the chesnut and the 
oak are pre-eminent as to durability ; and the 
chesnut affords rather more carbonaceous matter 
than the oak. 
In old Gothic buildings these woods have been 
sometimes mistaken one for the other ; but they 
may be easily known by this circumstance, that 
the pores in the alburnum of the oak are much 
larger and more thickly set, and are easily dis- 
Q 3 
