1 
: 
ee — 
578 
-%x other experiments he infers that mer- 
eury can combine with platina in fuch a 
manner as ‘nét to be feparated by the de- 
gree of heat necefiary to fufe the compound, 
Snce after the fufion it retains that proper- 
-ty, which is efientially characteriftic of the 
~prefence of mercury ima {olution of platina. 
“Another experiment is mentioned to prove 
that the aftion of mercury upon platina is 
~not confined to the metallic frate, but that 
this metal can combine- and form an iio- 
luble triple flt with an acid, which pro- 
duces a very foluble compound with pla- 
tina alone. The laf experiment: noticed 
3s intended to fhew that platina can retain 
- $n felution @ certain. quantity of mercury, 
-and prevent its redudtion by a lubftance 
which ats moft powerfully to that effect, 
when platina is not prefent. 
Mr. Chenevix challenges a fair and ftri& 
examination of the fubjed. “© The faéts,”’ 
' ays he ** contained in this paper cannot 
~ be (ubmitted to too fevere a fcrutiny, and 
mo judge can. be more rigid or more com- 
petent than the very perfon (Dr. Wrollafon 
we prefame) who was the firft to doubt my | 
former experiments. But it is neceflary to 
-be obferved by whcever fhall think them 
worth the trouble of verifying, that even 
thefe experiments are liable to fail unlefs 
proper precautions ars ufed: that I have 
never opera‘ed upon leis than one hundred 
grains; and that. the refults, which I 
have ftated, however fimple they may ap- 
pear, have been the-confant labour of 
fome weeks. 
Mr. KNIGHT, in a letter to Sir Jofeph 
Banks, has endeavoured to prove that the 
fap in trees, in an injpiffated { Rate, or fome 
eonerete matter depofited by it, exiftsdu- 
xing the winter in the alburnum or fap- 
wood, and that from this fluid, or fubftance, 
diffa}ved in the afcending aqueous fap is 
derived the matter which enters into the 
compofitionof the new leaves in the-{pring, 
and thus furnifhes thofe organs, which 
were not wanted during the winter, but 
which are eflential to the further progrefs 
ef vegetation. Hence the fuperiority of 
winter-felled wood, which has generally: 
been attributed to the ablence of the fap 
aé that feafos, is owing to the fubfance 
that has been added io it inftead of taken 
from it. 
_ Bulbous and tuberous roots are almot 
wholly generated after the leaves and ftems 
ef the plants,-to whica they belong, have 
attained their full-growth ; hence the pro- 
duce of meadows is greatly increafed when 
~ the herbage of the preceding year remained 
to perform its proper office till the end of 
the autumn, oa ground whien had beca 
Proceedings of Learned Societies. 
[July 1, 
mowed early in the fummer., On this ac- 
count Mr. Knight infers that the leaves 
‘both of trees and herbaceous plants, are 
alike employed, during the latter part of 
fummer, in the preparation of matter cal- 
culated to afford focd to the expanding 
buds and blofloms of the fucceeding {pring, 
and to enter into the compofition of new 
organs of affimilation. In proof of this 
hypothelis Mr. Knight made many expe- 
riments; an account of which. he has, by 
‘means of this letter, laid before the Royal 
Society. 
The avienees that bulbous and Pace . 
rooted plants contain matter within them-= 
felves is decifive; for they vegetate even in 
dry reoms, on the approach of {pring ; and 
many bulbous rooted plants produce their 
leaves and flowers with nearly the fame 
vigeur by the application of water only, 
as “they do when growing in the bet mould. 
The water probably adts only by difolving 
the matter prepared and depofited in the 
preceding year, dnd hence the root becomes. 
exhaufted and fpoiled; and. it has~been 
found that the leaves and flowers and roots 
“of fach plants afforded “no more carbon 
than exif in bulbous roots of the famre 
weight, the leaves and flowers of which had 
never expanded. 
From experiments made with care; Mr. 
Knight infers that the refervoir of matter 
depofited in the alburnum is not wholly 
exhaufted in the fucceeding, fpring, from 
which circumitance he. accounts for the fe- 
verai fucceffions of leaves and buds which 
trees are capable of producing, when thofe 
previoufly pro:rudéd have been deftroyed 
by infetts, or other -caufes; and for the. 
luxuriant fhoots, which often {pring from 
the trunks of the-trees, whole branches 
have been long in a ftate of decay. He 
thinks that the alburnum remains unem- 
ployed in fome cafes during feveral fie- 
ceflive years, fince it is not probable that 
i: can be employed by trees, which, after 
having been tranfplanted, prochice very 
few leaves, or by thofe which produce 
neither bioffems. nor fruit. In the year 
1802, Mr. Knight cut off in the winter ail 
the branches of a pear-tree, fuppofed to be 
Migarly 2co0 years old, and whofe extremi- 
ties were generally dead ; he pared eff, at 
the fame time all the lifelefs external bark. 
No marks of vegetation appeared in the 
following fpring; but in July numerous 
buds penetrated through the bark, and in 
the autumn every part was covered with, 
fhoots about two feet in length. The 
number of leaves and branches appeared ta 
exceed the whole of thofe, which the tree 
had borne 
which 
tag three preceding feafons, , 
