APPENDIX. 
561 
to the oxygen given off is influenced by the sun’s rays ; but that 
owing to the necessary exclusion of the external atmosphere during 
the progress of experiments, it is impossible, with any degree of 
accuracy, to calculate the volume of these evolved gases during 
any period of the growth of plants in their natural state. If to 
this indefinite quantity of nitrogen given off by plants, there be 
added that definite volume incorporated into their substance, the 
question arises, whence do plants derive their nitrogen, and does 
any part of it proceed from the atmosphere ? This problem Mr. 
Rigg has endeavoured to solve by a series of tabulated experiments 
upon seeds and seedling plants, the result of which is a large 
excess of nitrogen in the latter, and under such circumstances of 
growth that he is compelled to fix upon the atmosphere as its 
source. He has also arrived at the conclusion, that the differences 
which we find in the germination of seeds and the growth of plants 
in the shade and sunshine, are due in a great measure to the 
influence of nitrogen. 
