MURRAY ON THE COURSE OF THE SAP. 
13 
acid may be carried down into the earth by showers, and there put 
in a fit condition for the plant, which may then take it up by the 
roots. All that I say is, that it does not enter free into the plant 
through the leaves, and that the idea of its descending from them, 
and supplying the plant with carbon for its structure, infers an 
absolute impossibility. 
With a glance at one other class of experiments which bear on 
this point I have done. I do not know that Sachs has relied on it, 
but other physiologists have. It has been maintained that not only 
carbolic acid, but nitrogen free and uncombined, is taken up by the 
plant through its leaves, and it is plain that if the one can be so taken 
up there seems no very good reason why the other should not be also 
—possibly not so readily—but still, taken up. Both are constituent 
gaseous elements of the plant, and if it can take up the one by the 
leaves, it might reasonably be expected that it should also be able 
to take up the other. Now with nitrogen the question has been 
fairly tried by many first-rate chemists and physiologists, and a 
great multitude of experiments have been made, and although dis¬ 
crepancies have occurred on points which do not concern this ques¬ 
tion, I think I may say that, with one exception (De Villa, whose 
authority is nothing equal in weight to that of most of those opposed 
to him), the conclusion has been unanimous in the negative. It would 
be tedious to mention all the experimenters, but when I name Bous- 
singault as commencing the inquiry and Lawes and Gilbert ter¬ 
minating it, no question as to its efficiency can arise. The 
concluding words of Mr. Lawes are “in view of the evidence 
afforded of the non-assimilation of free nitrogen by plants under the 
wide range of circumstances provided in the experiments it is 
desirable that the several actual or possible sources of combined 
nitrogen to plants should be more fully investigated both quanti- 
tively and qualitatively.” 
In conclusion, I trust that others will repeat my experiments 
and weigh my arguments. It is a very self-confident thing for a 
man to set himself up in opposition to views entertained by all the 
heroes sciential of his own time, and although I own that I am not 
generally much troubled by reverence for authority, I still feel that 
I shall not be sure whether I have been wise or impudent in writing 
this paper until I have my experiments repeated and confirmed by 
independent workers. 
