PROFESSOR JOHNSTON S LECTURE. 
579 
rially improved during the last five years, was clear from a fe.w 
examples. It was known that the bodies of animals contained 
much nitrogen. This nitrogen they obtained from their food, and 
this food was all originally of vegetable origin. Now, vegetable 
food was found to be more valuable in proportion as the per centage 
of nitrogen was found to be greater; it came nearer to the nature of 
the animals themselves. It was thought that, by a proper arrange- 
ment of the manure, the farmer could regulate the quantity of 
nitrogen in his corn, and experiments were made in order to de- 
termine the point; but this opinion had not borne the test of rigid 
experimental and chemical criticism. He then mentioned some 
experiments which were made on the growth of turnips by Mr. 
Laws, and which were published in the eighth volume of the 
Transactions of the Royal Agricultural Society. The result of 
those experiments appeared to be that the proportion of nitrogen 
in the turnip might be increased by the application of manures 
containing nitrogen. This report was valuable in itself, and an 
addition to our theoretical probabilities, but it did not afford us 
any more ground to speculate upon. * * * 
He had stated a number of points in regard to which the union 
of scientific investigation in the laboratory with the experiments 
in the garden would lead to important results in connection with 
many important points relating to the theory of agriculture, all of 
which have a most important bearing upon practical agriculture, 
as he might shew if he had time. Several gentlemen here called 
out “Go on;” but the lecturer declined acquiescing, for the reason 
that he was not accustomed to address a large audience except 
from written notes. 
Among these theoretical points, more important if possible than 
the questions he had previously treated of, were the questions in 
regard to the nitrogen of plants. What were the natural sources 
of nitrogen which all plants required! How much did they need! 
What functions did they perform in nature! How much remained 
in the plant! How much escaped into the air from the leaves! 
All these were questions having an important practical bearing, to 
the solution of which a high degree of importance w*as attached. He 
would explain in part how this arose. Nitrogen was acknowledged 
to be an important part of the food of plants, as it contributed to the 
formation of those substances upon which the production of muscle 
in animals was supposed to depend. Nitrogen had hitherto been 
supposed to remain for the most part in plants, but recent experi- 
ments in the United States had shewn that plants constantly gave 
off nitrogen in large quantities from their leaves. It appeared 
probable that nitrogen entered into plants by the roots, and that 
only a small proportion was left at last in the full grown plant com- 
