249 
GARDENING AS A SCIENCE. 
VEGETABLE PHYSIOLOGY.— No. XL 
We close this series by a few observations on tlie nature and offices of 
Manure, as connected with the nutrition and growth of plants. There is no 
other subject in the philosophy of agriculture and horticulture which has been so 
little understood, so involved in contradiction and bewildering conjectures. 
Our remarks cannot extend to agriculture, otherwise we should find a rich 
store of materials. Horticulture, however, is not a barren field ; and if we have 
succeeded in the previous articles to elucidate the theories of vegetable organi- 
sation and function, there will be the less difficulty in appreciating the phenomena 
assimilation, on which the discoveries of modern chemistry have thrown much 
light. 
It has been seen that the ultimate elements of structure are few ; that four 
of them are organic — in other words, capable of uniting under various forms— 
and in these forms constituting not only organic structure, but, in many instances, 
the products of that structure. Thus, 1st. Oxygen and hydrogen, from a gaseous 
form, unite and become liquid water. Water enters into the fluid products of all 
.plants. 2nd. Hydrogen and nitrogen form ammonia. 3rd. Carbon and oxygen 
unite in the form of carbonic acid gas ; and carbon is the base of lignin and of 
woody fibre. Now, all these organic elements— being originally gaseous — exist 
in, and may be derived from, the air ; but, as we find potass, soda, chalk, 
muriatic acid, iron, &c. &c., not one of which can, under ordinary circumstances, 
be referred to the atmosphere, we must refer them to another medium, and that is 
the ground. These substances, therefore, and some others, are inorganic ; and, as 
such, are found in the ashes of plants, having resisted the action of fire that had 
decomposed and gasified the substances which in themselves are the products of 
the organic structure. 
In a former article it was stated that every substance which combines the four 
organic elements, under whatever name it pass, is bond fide a manure. Thus, the 
vegetable portion of black heath-mould is manure ; the other ingredient being 
sand, which is not decomposable under ordinary conditions, and, therefore, is 
inorganic. This sand is silej^, one of the chief constituents of granite ; but, by 
the action of potassa, it is attracted to that alkali, and uniting with it, becomes 
soluble silicate of potassa. 
Some persons have supposed that pure flint is solid oxygen ; and that able 
chemist, Mr. Hume, wrote a small treatise on the subject, wherein he supported 
his hypothesis by many facts, ably and pertinently adduced. If oxygen be a 
modification of electricity, flint and crystal are two of the most powerful electrics 
to which we can appeal. 
Humus has for some years been the fashionable term by which modern writers 
VOL. XI. NO. CXXXI. KK 
