CULTURAL CHEMISTRY. 
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was conveyed into the organism, bad long been a subject of physical inquiry ; the 
vessels and cells had been discovered, and to that great man, Thomas Andrew 
Knight, we were indebted for the suggestion, that " it is through the channels of 
the cells that the sap ascends." At the same time it was demonstrated, that not 
one particle of solid matter could by possibility pass into the absorbent vessels. 
So far, every inquiry bore upon the roots, as the channels of absorption ; but when 
the theory of introsusception of gases by the leaves (carbonic acid gas in particular) 
was broached, it at once became a sine qua non, and as Mr. Johnston observed — the 
opinion prevailed, and was extensively acted upon by some, that " plants obtain all 
their organic matter directly from the air ; and derive, and therefore required, only 
mineral matter from the ground ;" and in a note he thus quotes Liebig's words : — 
" The crops on a field, diminish or increase, in exact proportion to the diminution or 
increase of the mineral substances conveyed to it in manures." Thus, bones were 
burned in order to destroy their animal matter and mucilage, with a view to retain 
the dry and indestructible phosphate, and carbonate of lime. "But this mineral-matter 
opinion has also received its death-blow, and we are again on the old highway of 
experience taking theory into our counsels, appointing him our consulting chemist, 
but not allowing him to overrule our deliberations." 
Ammonia has had vast importance attached to it, since Professor Liebig assumed 
the lead in the field of Agriculture. It is a natural compound of hydrogen and 
nitrogen, and assuredly exists in the atmosphere ; its elements abound in animal, 
and in some vegetable substances, and these combine during the process of decay, 
and are extricated in the form of ammoniacal gas. Modern theory has taught that 
plants derive all the nitrogen they contain, from the ammonia floating in the atmo- 
sphere. " This opinion was so contrary to the oldest, and most common experience 
of practical men of all grades of intelligence, that nothing but the announcement of 
it in the form of an undoubted law, could have secured it any degree of permanent 
consideration, even among scientific men. As it was, sanguine young persons, 
chiefly such as were unfamiliar with practice, took it up, and warmly maintained it 
both in this country and abroad. A calm consideration of facts, however, is 
gradually removing this notion from the public mind, and another year or two will 
banish it from our books." 
These facts may be detailed in a very few lines. Ammoniacal gas is of itself 
destructive when applied to leaves. A Cape Jasmine (Gardenia) was infested with 
the mealy insect. A glass vessel being inverted over the plant in its pot, a drop or 
two of weak ammoniacal solution was introduced at the bottom. In a few seconds, 
the entire foliage assumed the richest imaginable dense green. But this beautiful 
appearance was the precursor of destruction. Time was given to let the vapour act 
upon the insects, yet the experiment occupied only two or three minutes. The 
glass was raised, the blue-green of the leaves subsided, and was rapidly succeeded 
by the withered brown hue of death. Ammonia, then, and indeed every species of 
gas unnatural to plants, must be viewed with a jealous eye. Manures contain more 
