266 SCIENCE PROGRESS 



with the fungus and the chief purpose of this union should be 

 endangered. 



The union depends likewise upon the power, in which the 

 fungus is predominant, of disintegrating, by both mechanical 

 and chemical means, the rocks upon which lichens are often 

 growing. The lichen, as is well known, is a pioneer as a soil- 

 former. According to Dr. O. Darbishire, if bare rocks are 

 found in the neighbourhood of the Poles themselves there is 

 little doubt that lichens will be found growing there. Many of 

 these rock-lichens are distinguished by an astounding longevity. 

 The bare rock, I would add, supplies the ideal food of the 

 lichen. At one time eminent philosophers believed the lichen 

 to be created out of solid rock. The point of importance 

 is that the soil is generally enriched by the work of the strictly 

 cross-feeding, symbiotic lichen. 



The same may be said of the clover, a plant which will grow 

 on bare places, provided the right minerals are obtainable, 

 and which is similarly remarkable for its symbiotic alliances. 

 As regards melilotiis, or sweet clover, an American writer, 

 Mr. E. E. Miller, states : "In the limestone sections it has 

 become the first-aid crop of the most depleted soils. On land 

 so poor in humus and nitrogen that practically no other crop 

 will grow, sweet clover thrives. Being a legume, and an 

 uncommonly vigorous one, it takes it but a few years to store 

 up in the soil sufficient nitrogen, and to furnish by its own 

 growth and decay sufficient organic matter to make the land 

 fertile enough for any of the staple crops." 



Of Lespedeza, or Japanese clover, he says : " The good it 

 has done by holding and enriching old fields and waste lands 

 which, but for it, would have washed away or grown up with 

 really harmful weeds, no man can accurately estimate. It 

 has literally been the salvation of hundreds of thousands of 

 acres of land all over the Cotton Belt and north of it." 



Amongst cross-feeding, symbiotic, and widely useful bac- 

 teria, there is the case of Nitroso Monas, living on ammonium 

 sulphate, taking its energy from the nitrogen of ammonium, 

 and forming nitrites. Living with it in Symbiosis is Nitro- 

 bacter, using the nitrites formed by Nitroso Monas, and 

 oxidising them into nitrates. These nitrates are of great im- 

 portance. Without the primal industry of Nitroso Monas, 

 the Symbiosis with Nitrobader would be impossible, and without 

 the succession of ever higher but similar forms of life-part- 

 nerships based upon it, the evolution of the highest forms of 

 life would have been impossible. All important pioneer work 

 is thus done on cross-feeding. Strenuous work cum symbiotic 

 cross-feeding provides the capital on which race after race of 

 higher organisms is reared. 



