201 
GARDENING AS A SCIENCE. 
No. IX. 
From the subject of the nutriment of plants obtained by the decomposition of 
vegetable matter, chiefly, the mind is naturally led to the investigation of those 
vessels or organs which receive the fluids from the earth, and elaborate the several 
products essential to the plant, and specific to it. But here we are at sea. Every 
attempt has failed to determine what the crude sap really is ; and we are equally 
at a loss to settle the question, whether the leaves are absorbent as well as trans- 
piratory organs. 
Certain it is, that chemistry, as a science of analysis, is utterly powerless to 
solve the mysteries of vital assimilation : and we deem it little better than waste 
of time to advance one conjecture on the ground of any influence that can be 
drawn from the analysis of gums, resins, salts, sugar, bitter principle, or colouring 
matter, &c., the effete productions of organized life. 
Still, Science acquires importance by the able researches of philosophers ; and 
having before us several invaluable manuscripts of the late President, Mr. Knight, 
we hope our readers will be gratified by the perusal of a few extracts, which will 
prove to what extent the laborious and profound investigations of that great man 
were carried. 
The name of the celebrated Dutrochet may yet be familiar with many : he 
was a correspondent of Mr. Knight, and once visited him at Downton Castle. 
Mr. Knight thus recites an experiment by which the French philosopher at one 
time thought he could throw some light upon the phenomena of the sap : — " M. 
Dutrochet has made some very singular, and, I think, important discoveries, which 
show that the power which causes lighter fluids to pass through animal and vege- 
table membranes is very wonderful. He bound three folds of recently extracted 
bladder round the bottom of a tube of glass, and through these folds, under ordinary 
circumstances, no fluid could pass ; but upon a solution of one part of sugar in two 
parts of water being put into the glass tube, the water " (contained in another 
glass vessel wherein the tube was placed) " passed rapidly through the three folds 
of bladder, not only in opposition to gravitation, but in opposition to that of the 
pressure of a column of forty-five inches of mercury, nearly equivalent to a pressure 
of twenty-two pounds and a half upon an inch square, and of fifty feet perpen- 
dicular of water. I had previously proved that the specific gravity of the sap of 
trees in the spring, increases in proportion to its distance from the ground, and that 
a good deal of saccharine matter is found in the alburnum of trees in the spring, 
which contained none in the winter." 
M. Dutrochet resided with Mr. Knight nearly three weeks, and both gentlemen 
arrived at the conclusion — "that the water and nutriment absorbed from the soil 
VOL. X. CXVII. D D 
