MICROSCOPIC GARDENING. 



17 



quantities accumulating from other animals, which must be far 

 greater, it is easy to see that whether regarded as locked up 

 nitrogen, or as merely accumulating material, the blocking up 

 of the earth's surface, so far as man is concerned, would be 

 rapid. 



Another set of soil organisms are found to bring about the 

 oxidation of ammonia salts to salts of nitrous and nitric acids, 

 forms in which they are even more available to the roots of the 

 higher plants. They thus supplement the action of those 

 organisms which convert urea into ammonium salts, as well as 

 those of a large class of forms which convert organic nitrogenous 

 bodies such as horn, hair, and other animal remains, and the 

 debris of plants into ammonia. 



These nitrifying organisms are among the most interesting 

 and important of all the soil-organisms, and the ingenious 

 methods of microscopic gardening which have led to their isola- 

 tion and culture have opened up entirely new vistas into unknown 

 regions in plant physiology, as well as thrown brilliant light on 

 hitherto obscure problems in practical agriculture and horticul- 

 ture. Equally important are the discoveries recently to hand 

 concerning a series of minute soil organisms, which, alone or in 

 symbiosis with Leguminous or other plants, fix the free nitrogen 

 of the air, and of others which undo the work and set nitrogen 

 free again, so that our picture of the cycle of nitrogen in nature 

 is now fairly complete in its outlines, a fact the significance of 

 which only attains its proper proportions when we know how 

 difficult that problem was in the past, and how far-reaching its 

 consequences are. 



These are only a few of the results already to hand. 

 Microscopic gardening has unearthed the forms which cause the 

 rotting of flax, the decomposition of sulphur compounds and 

 iron-salts, and which bring about numerous other changes in 

 soil ; it has also brought to light all kinds of disease-germs — 

 forms fatal to man and other animals, as well as to plants, of 

 which I may mention "finger and toe," the "smuts" of corn, 

 damping off of seedlings among others. It has taught us to 

 appreciate, even more in detail than Darwin's beautiful book 

 had already taught us, the enormous influence of earthworms in 

 soil, for these animals bring up from depths at which they are 

 inert and useless, germs which can again do their work at the 



