144 Transactions. — Miscellaneous. 



atmosphere, and the infective organisms and the putrefactive 

 ones have been displaced by the normal earth dwellers, the 

 nitrifiers. 



I should mention here two varieties of bacteria which also 

 live in the earth, and have their influence on the nitrogen for 

 plant-food. One of these carries the reducing process too far, 

 as it breaks up the nitrites into the simple elements and 

 allows the nitrogen to escape back into the atmosphere, so 

 that plants lose it. But there is the other variety, which 

 reverses the process, taking up free nitrogen from the air and 

 building it up into organic bodies. This form is found in the 

 nodules which grow 'on the roots of leguminous plants, the 

 nodules being formed by the germs in their growth. By thus 

 utilising the atmospheric nitrogen these bacteria enable the 

 legume to live in a poor soil, and the value of cropping with 

 these plants is apparent, as by ploughing them in the soil is 

 greatly enriched. This particular nitrogen-collecting bac- 

 terium can now be bought as a substance called "nitragen," 

 and sown on the land. 



Disinfecting the Soil. 



The last of the organized material to disappear is, of 

 course, the bones in animals and the woody fibre in plants ; 

 but they, too, ultimately decay, and are dissolved and utilised 

 by the soil. In the process of " humification " — as this action 

 of the surface earth has been called — many earth insects and 

 worms play the part of tillers by turning over the upper 

 layers, passing it through their bodies, exposing fresh layers 

 to the action of air and light, just as the farmer does with his 

 plough, leaving it pulverised, oxidized, and enriched. When 

 we realise how the rich upper layers of the soil teem with this 

 useful insect and bacterial life we understand why it has been 

 spoken of as the " living humus," and we realise the import- 

 ance of moisture and air, and how flooding with water may 

 stop its vital processes — drowning it, as it were. In a de- 

 serted stockyard, tramped down and consolidated by the feet 

 of cattle in wet weather and baked hard by the sun in dry, 

 the air cannot penetrate the earth, and grass will not grow in 

 spite of the presence of abundant manure. But in course of 

 time the earth cracks by frost or drought, the worms begin 

 to turn it over again, air enters, and the humifaction of the 

 manure starts afresh. 



Under Water. 



In streams and ponds the same process of reduction of 

 complex organic waste takes place. Other forms of bacterial 

 life are at work dissolving it, and water-plants, such as cress, 

 duckweed, seaweed, and so on, are ready to absorb the 



