Mar..1906.] | BOTANICAL SOCIETY OF EDINBURGH. 187 
The question then arises-—-At what part of the plant does 
this proceed ? 
How Mr. Jamieson arrives at his discovery of the organs 
of fixation in green plants is illustrative of the faulty data 
underlying his hypotheses. 
The root cannot be an agent, he says, because the root in 
the soil is practically excluded from air. This, it will be 
recognised, is far from the fact. 
Mr. Jamieson says further that the stem cannot be the 
organ, because it has often an impervious bark. But we 
know that the young stem has a superficial structure not 
unlike that of the leaf. 
Mr. Jamieson then fixes upon the leaves as the organs by 
which the plant absorbs and fixes nitrogen, and he is 
strengthened in this view by the fact that the leaf absorbs 
carbonic acid gas and is also the absorber of what the plant 
chiefly requires, namely, water. But there is one fact in 
plant physiology that has been definitely established, it is 
that the leaf does not absorb the water which the plant 
requires. 
Having made up his mind that the leaves are nitrogen- 
fixers, Mr. Jamieson then seeks for direct evidence of special 
arrangements for the work. These he finds in the hairs which, 
as everyone knows, cover fréquently young leaves and stems, 
disappearing sometimes as the shoot matures. The contents 
of these hairs showed, by their reaction to certain chemical 
tests applied by Mr. Jamieson, and which more or less 
consistently indicated the presence of nitrogen, that a 
nitrogenous substance which he called albumen was present. 
To Mr. Jamieson the whole matter was clear; it was the 
solution of the question of the fixation of nitrogen from the 
air; whence could the nitrogen of the albumen reach the 
hair but from the air? There was free nitrogen in the air; 
these hairs were more or less exposed to the air; these hairs 
contained a nitrogenous substance; therefore the nitrogenous 
substance was formed by fixation of the air-nitrogen. 
Having assumed that green plants fix air-nitrogen ; having 
assumed that green chlorophyll has to do with it; having 
assumed that fixation takes place in the leaf, and having 
seen nitrogenous substance in certain hairs on the leaf, 
Mr. Jamieson names the hairs albumen generators, and 
