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. 



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. 11 



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). 12 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 



5o 



