456 



SCIENCE. 



[N. S. Vol. XXII. No. 563. 



the ratio of carbon to nitrogen in the ac- 

 cumulation being about 18 to 1 and 12 to 1, 

 respectively. 



Henry has also shown that the shed 

 leaves of many forest trees during their 

 decay may bring about the fixation of 

 nitrogen; and this fact, which again de- 

 pends on the oxidation of the carbohydrates 

 of the leaf to supply the necessary energy, 

 has been confirmied in the Rothamsted 

 Laboratory, as well as the presence of 

 Azot'obacter on the decaying leaf. 



It is obvious that one of the most inter- 

 esting fields for the study of these organ- 

 isms must lie in the virgin lands of a coun- 

 try like South Africa. We all know that 

 virgin soil may, on the one hand, represent 

 land of almost perpetual fertility; on the 

 other, it may constitute wastes of any de- 

 gree of sterility. What are the conditions 

 under which ensues that accumulation of 

 humus whose nitrogen will become avail- 

 able under cultivation, the 'black soils' 

 famous in every continent? The ecolog- 

 ical botanists are working out some of the 

 great climatic conditions, the amount and 

 distribution of rainfall and temperature 

 which are associated with 'steppe' areas of 

 great accumulated fertility, but the bac- 

 terial flora which is fundamentally bound 

 up with the problem remains as yet unex- 

 plored. 



It is possible also that on some of the 

 newer lands this and kindred bacteria are 

 absent because the conditions are not en- 

 tirely suitable to their development. A. 

 Koch has shown that the presence of cal- 

 cium carbonate is necessary to the action 

 of Azotohacter, and determinations of the 

 power of soils from the various Rotham- 

 sted fields to induce fixation confirm his 

 results, the development of the organism 

 in question being feeble when the soil was 

 derived from some of the fields that had 

 escaped the 'chalking' process to which the 



calcium carbonate of the Rothamsted soils 

 is due. 



The value of calcium carbonate in this 

 connection only adds to the many actions 

 which are brought about by the presence 

 of lime in the soil— lime, that is, in the 

 form of calcium carbonate, which will be- 

 have as a base towards the acids produced 

 by bacterial activity. The experimental 

 fields at Rothamsted afford a singular op- 

 portunity of studying the action of lime, 

 since the soil, a stiff, flinty loam, almost 

 a clay, is naturally devoid of calcium car- 

 bonate, though most of the cultivated fields 

 contain now from 2 to 5 per cent, in the 

 surface soil, due to the repeated applica- 

 tions of chalk, which used to be so integral 

 a part of farming practise up to the middle 

 of the nineteenth century. Where this 

 chalking process has been omitted, as is the 

 case in one or two fields, the whole agri- 

 cultural character of the field is changed: 

 the soil works so heavily that it is difficult 

 to keep the land under the plough ; and as 

 grass land it carries a very different and 

 altogether inferior class of vegetation. 

 On the experimental fields it has been pos- 

 sible to measure the rate at which natural 

 agencies, chiefly the carbonic acid and 

 water in the soil, are removing the calcium 

 carbonate that has been introduced into 

 the surface soil, and it is found to be dis- 

 appearing from the unmanured plots un- 

 der arable cultivation at an approximate 

 rate of 1,000 lbs. per acre per annum; a 

 rate which is increased by the use of 

 manures like sulphate of ammonia, but 

 diminished by the use of nitrate of soda 

 and of dung. Failing the renewal of the 

 custom of chalking or liming — and its 

 disuse is now very general — the continuous 

 removal of calcium carbonate thus indi- 

 cated must eventually result in the de- 

 terioration of the land to the level of that 

 which has never been chalked at all, and 

 even a state of sterility will ensue if much 



