138 The Romance of Wild Flowers 
contain a large percentage of nitrogen as contrasted 
with the predominating carbon compounds of the 
cereals. ‘The question whence this great quantity of 
nitrogen was derived was long a problem to agricul- 
tural chemists, for it was found by the valuable experi- 
ments of Lawes and Gilbert at Rothamsted that whilst 
in most crops the nitrogen they yield can be accounted 
for by the amount of manure supplied to the land, 
with the addition of that contained in rain-water, 
when it came to an analysis of Peas, Beans, Vetches, 
etc., an excess of nitrogen was found beyond what 
could be accounted for in this manner. The only 
explanation that occurs is that the free nitrogen 
existing in the atmosphere is laid hold of and 
assimilated by the growing plant; but experimental 
botanists of high authority have been agreed that the 
plant has not this power, that though nitrogen enters 
freely into the air-spaces in the leaves the plant 
cannot avail itself of this clement—it can only extract 
it by root-action from the soil in the form of ammonia 
and nitric acid. 
One of the most startling of the recent disclosures 
concerning the micro- 
organisms was the 
discovery of bacteria 
capable of living in 
soil utterly devoid of 
all animal or vegetable 
matter, and by their 
feeding upon the 
purely mineral con- 
stituents of the soil, 
and passing them through their bodies to give such 
Bacteria nodules on roots of White 
Clover 
