THE ORGANISMS OF THE SOIL 159 



phosphates but on taking samples of the soil after a spell of 

 drought they are found to be in the insoluble form. When, 

 however, the fields are watered and brought under cultivation, 

 then on analysis the soil shows a high percentage of soluble 

 phosphates. There may be other means of explaining this 

 phenomenon but the one which suggests itself to any one 

 acquainted with bacteria in the soil and their life history is 

 that the solubility of the phosphates is brought about by the 

 action of bacteria. When the soil becomes dry and parched 

 the bacteria encyst or retire into minute horny capsules and 

 their activities cease ; when water is supplied to them, the 

 capsules absorb water and burst, freeing the rested organisms, 

 which straightway start propagating at the very rapid rate 

 observed in such organisms. 



This explanation is founded on analogy ; but then similar 

 analogies have been proved to be actual facts in case of carbon, 

 nitrogen and sulphur and it is likely to prove so, judging 

 from Prianischnikoffs experiments, in the case of the last 

 essential constituent of protoplasm. If it be so, then it is one 

 of the most beautiful examples of the manner in which Nature 

 preserves her most precious assets against the proper time. 



We come then to regard the organisms of the soil as the 

 inhabitants of the globe persisting from a period when it was 

 still impossible for the higher plants and animals to live upon 

 it. We can imagine the earth to have been in such a state as 

 Treub found the island of Krakatoa in 1886, three years after the 

 great eruption, when the primitive rocks were teeming with 

 microscopic life. In Krakatoa the whole island had been 

 reduced to a mass of glowing ash ; but still, after a short 

 interval, the surface became slimy with micro-organisms busily 

 breaking down the silicates and forming a soil which the 

 higher plants, later on, would take advantage of. In the early 

 history of the earth the soil became similarly formed but 

 aeons of time had to pass before the higher plants became 

 developed and were able to take advantage of the habitat 

 prepared for them. Heat, which kills most living beings, was 

 no hindrance, for the blue-green algae live in nearly boiling water 

 to-day in the hot springs; 1 food, as we understand it, these 

 organisms did not require, as they obtained their supplies 



1 As far as I can discover the highest recorded temperature is 85 ° C. : 

 A. Engler and K. Prantl, Die Nat. Pflauzenfam, 1. Teil, Leipzig, 1900, p. 63. 



