406 MR. R. RIGG ON THE EVOLUTION OF NITROGEN 



tuting an atmosphere with a decided preponderance of nitrogen and a much smaller 

 proportion of oxygen. 



Finding that plants under different circumstances of growth differ in the relative 

 quantity of nitrogen which they contain, as well as in the other elements which enter 

 into their constitution, I was desirous of obtaining information which would lead us 

 to account for the well-known fact of plants increasing most in size during cloudy 

 weather, and of grasses, for instance, which are shaded (as under hedges), increasing 

 much in straw, but producing seed both small in quantity and inferior in quality. 



By way of commencement in this part of the research, I made duplicate experi- 

 ments with the same kind of seeds, steeped them in and supplied them with the same 

 kind of water, and kept them under equal circumstances in every respect, except that 

 of placing one of each in the sun's rays in the greenhouse, where the sun shone till 

 three p.m., and the other in the same situation, excluded however from the sun's rays, 

 but not from the light. Those in the shade increased in length much more than the 

 others, were a little lighter in colour, and when weighed before they were exposed to 

 the drying temperature, were also heavier, but when dried at 100° to 110° were con- 

 siderably less in weight. The ultimate analyses of these experiments are found in 

 Table XL, and the result of the experiments as regards nitrogen is, that those plants 

 which weighed the heaviest before drying, and which had as it were moulded into 

 shape the largest quantity of matter in the form of plants, contained, in the cress for 

 instance, 147 parts of nitrogen for every 1000 parts of carbon ; whereas those plants 

 from seed of the same kind which grew in the sun's rays, and whose weight before 

 drying and when freed from foreign water was nine per cent, lighter than the other, 

 contained only 111 parts of nitrogen for 1000 of carbon; — and in addition I might 

 make an observation which is in perfect harmony with all that has been noticed upon 

 the influence of nitrogen on the growth of plants, viz. that whereas the cress arrived 

 at its state of maturity, so far as the seed could furnish it with nourishment, in 

 eighteen days, the rape had not exhausted all its seed in twenty-six days; and the 

 proportionate quantity of nitrogen in those plants was, in cress in the sun's rays 

 111, in rape in the same situation 73 ; and in cress in the shade 147, and in rape 82, 

 when compared with 1000 parts by weight of carbon in each. 



In concluding this subject, upon which I have been as brief as its nature would 

 admit of, not even entering at all upon the practical application thereof, the point 

 of view wherein its real value consists, I beg to observe that, although nitrogen ap- 

 pears from these experiments to be a very powerful agent in the economy of plants, 

 it is far from my intention to give it any undue importance. It is my object to draw 

 attention to an element which, comparatively speaking, has escaped unnoticed, and to 

 vindicate the necessity of a most scrupulous attention to those products which, though 

 so minute in quantity as to be with difficulty detected in our balances, have never- 

 theless been wisely assigned to discharge the most important functions. 



