THE NEW SOIL SCIENCE. 



71 



and from the air in the interstices of the soil ; and both these gases, it is 

 stated, are absorbed through the roots. Experiment and experience have 

 shown that over and above these substances and gases the most important 

 food material required by plants is nitrogen ; yet it has been demonstrated 

 that a plant cannot absorb or obtain it in the same manner in which it 

 obtains its carbon or carbonic acid, viz. by absorption through the leaves ; 

 nor can the plant take nitrogen in as nitrogen (with the exception of the 

 flesh-feeding plants) through its roots ; and yet a plant would perish unless 

 nitrogen existed in some combined form (the nitrates and compounds of 

 ammonia) in the soil, and in a state readily obtainable by means of its 

 roots. 



Experience, on the other hand, has also taught cultivators that though 

 nitrogen was such an important factor and so difficult to obtain by 

 plants, yet there were a number of cultivated plants that could obtain 

 it somehow, and that when grown in a rotation or otherwise they left the 

 land in a better condition in respect to nitrogen contents than before. 

 Wheat, Rye, Oats, Barley, Potatos, Beet, Tobacco, Buckwheat, Mustard, 

 Cabbage, and Vines have long been noted as nitrogen consumers because 

 they drew large amounts of nitrogen from the soil, thus leaving the land 

 poor and worn out after repeated croppings. These plants practically 

 suffer from starvation, it was found, if the soil does not contain a suf- 

 ficient supply of available nitrogen, and therefore this plant-food substance, 

 if it was deficient, had to be artificially supplied. On the other hand, 

 Peas, Beans, Vetches, and Clover, it was noted, did not respond to 

 applications of nitrogenous manures, yet apparently they could obtain 

 nitrogen by some natural means, and as such plants actually increased the 

 amount of nitrogen in the soil they were practically regarded as nitrogen 

 producers. Since the attention of observers and experimenters has been 

 directed to the germ life of the soil, the study of which, as a special 

 branch of bacteriology, constitutes the " new soil science," we now have 

 some idea how such plants are able to obtain the requisite nitrogen. 



The study of bacteriology as a science has within the past twenty years 

 made a marvellous advance. It is a study that appeals to the imagina- 

 tion of the public, dealing as it does with our invisible friends and foes. 

 The subject has, in fact, made such an advance that " bacteria " to-day 

 is a common household word. We have of course used bacteria abundantly 

 in the past, but till recently we were unaware that we were doing so, 

 and their action was attributed to chemical and physical causes. The 

 fermentative industries, termed by Professor Marshall Ward " the oldest 

 form of microscopic gardening practised by man," such as brewing and 

 vinegar making, depend on the action of bacteria ; so do the maceration 

 industries— i.e. the retting of Flax, Jute, and Hemp. To bacteria we 

 owe the preparation of indigo and opium, the curing of Tobacco, the 

 cleaning of sponges, the preparation of citric acid, and our butter and 

 cheese. 



We now know, through bacteriological research, that instead of being- 

 dead inert matter the soil is literally teeming with micro-organic life, and 

 it is estimated that from one to two hundred millions of germs may be 

 present in a single ounce of soil. It must be acknowledged that as yet 

 we know but little of this soil life, but as far as we have progressed the 



