694 The Sources of the Nitrogen of oi.ir Legtminoiis Crops. 
the point of maximum accumulation had been reached, and lastly 
■when the seed was nearly ripe. Each of the eight descriptions 
of plant was grown in sand (with the plant-ash), watered with 
the extract from a rich soil ; also in a mixture of two parts rich 
garden soil and one part of sand. The pits with their plants 
were exposed to the open air, but protected from heavy rain. 
In the sand the infection was comparatively local and limited, 
but some of the nodules developed to a great size on the 
roots of the weak plants so grown. In the rich soil the infection 
was much more general over the whole area of the roots, the 
nodules were much more numerous, but generally very much 
smaller. Eventually the nodules were picked off the roots, 
counted, weighed, and the dry substance and the nitrogen in 
them determined. 
Taking the peas as typical of the annuals, and the sainfoin 
of the plants of longer life, the general result was that, at the 
third period of growth of the peas in sand, the amount of dry 
matter of the nodules was very much diminished, the percentage 
of nitrogen in the dry matter was very much reduced, and the 
actual quantity of nitrogen remaining in the total nodules was 
also very much reduced. In fact, the nitrogen of the nodules 
was almost exhausted. The peas grown in rich soil, however, 
maintained much more vegetative activity at the conclusion, 
and showed a very great increase in the number of nodules from 
the first to the third period ; and with this there was also much 
more dry substance, and even a greater actual quantity of nitro- 
gen, in the total nodules at the conclusion. Still, as in the peas 
grown in sand, the percentage of nitrogen in the diy substance 
of the nodules was very much reduced at the conclusion. 
In the case of the plant of longer life, the sainfoin, there was, 
both in sand and in soil, very great increase in the number of 
nodules, and in the actual amount of dry substance and of nitro- 
gen in them, as the growth progressed. The percentage of 
nitrogen in the dry substance of the nodules also showed, even 
in the sand, comparatively little reduction, and in the soil even 
an increase. In fact, separate analyses of nodules of different 
character or in different conditions showed thnt, whilst some 
were more or less exhausted and contained a less percentage 
of nitrogen, others contained a high percentage, and were doubt- 
less new and active. 
'J'hus, the results pointed to the interesting conclusion that, 
in the case of the annual, when the seed is formed, and the 
plant more or less exhausted, both the actual amount of nitrogen 
in the nodules, and its percentage in the dry substance, are 
greatly reduced ; but that, with the plant of longer life, although 
