126 
Sydney H. Vines. 
Distilled water . . . 1000 grammes. 
Potassiurn nitrate . 1 » 
Calcium sulphate . . 0.5 » 
Magnesium sulphate . 0.5 » 
and a trace of calcium phosphate. 
After having grown for a few days under these conditions, the lea- 
ves of the young plants, though perfectly vigorous, began to assume a 
yellow colour. A small quantity of ferrous sulphate was then added to 
the liquid contained in some of the vessels, and the leaves of the plants 
growing in those vessels rapidly assumed their normal green colour. When 
the plants had grown for a week in the glass vessels, the leaves of those 
whieh had grown in Solutions containing no iron were of a pale yellow 
colour, and some were even white, but in every other respect they were 
similar to those of the plants whieh had grown in the Solutions to whieh 
iron had been added. 
This experiment is merely a repetilion of a process whieh frequently 
occurs in nature. Il is not an uncommon occurrence in gardens, that trees 
or shrubs turn yellow', become chlorotic, as it is termed, and il is well- 
known, from the observations of Gris, father and son, of Sachs and of others, 
that this condition is a consequence of an insufficienl supply of iron. 
That this is so is proved by the fact that the chlorosis can be removed 
b\ watering the plant with dilule Solutions of iron salts. Here, then, 
are mauy instances of the growth of leaves under circumstances whieh 
prevent assimilation. 
ln concluding the discussion of this part of the subject, a brief sum- 
mary of the results obtained may be given. lt has been shewn, 
1) that leaves can grow' in blue light, 
2) that they grow in an atmosphere containing no C0 2 , 
3) that they grow although they contain no Chlorophyll. 
Now it is admitted on all hands that for the performance of the 
function of assimilation the following conditions are necessary: 
1) the presence of the less refrangible rays of the spectrum, 
2) the presence of CO-i in the surrounding medium, 
3) the presence of Chlorophyll in the assimilating organs. 
In the foregoing experiments one or other of these conditions was 
left unfultilled, and therefore the leaves did not assimilate. But it is un- 
deniable that they grew. The obvious conclusion is that the theory of 
the »self-nutrition« of leaves is contradicted by experimental evidence. 
