The First Land Plants 
All these rootlets and fungi are searching and prob- 
ing patiently every film of moisture and absorbing the 
salts contained in it. P 
Now and again a worm is encountered stolidly eating 
its way right onwards and swallowing all sorts of vege- 
table, animal, and mineral matter. Inside its body 
there are chalk glands and bacteria which are working 
up its aliment, and the residue will form the worm-casts 
deposited on the surface when the worm comes up in 
the evening. 
The circulation of air in these underground passages 
and grottos is rapid and complex. 
Everything alive is breathing in oxygen and giving 
off carbonic acid. The more oxygen there is the more 
energetic and intense is the life of every microbe and 
fungus and root and worm and insect, So, for instance, 
the azotobacter will form more nitrate, the worm will 
eat faster, and the roots will absorb more water." 
As all these living things are taking in oxygen they 
must, necessarily, give out carbonic acid, which will be 
evaporating from the surface. The bacteria of one 
hectare would alone give off some 75 kg. per day (that 
is, 165 lbs. per acre nearly).” This will go to replenish 
the carbonic acid supply of the green leaves. But some 
of the carbonic acid given off by, roots and by fungi 
is employed in rendering soluble such refractory and 
stubborn minerals as silicates and aluminates which con- 
tain perhaps minute particles of valuable salts. This 
is another and unexpected “fitting reaction,” for the 
carbonic acid is a waste product, and yet it is used to 
furnish food to the living plant! 
Now suppose heavy rain falls steadily and for days 
together ; the soil is saturated, so that the air is ex- 
hausted and perhaps millions of bacteria unintentionally 
commit suicide by carbonic acid poisoning. Others 
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