158 SCIENCE PROGRESS 



oxygen. This zone occurs at a depth of about 200 fathoms. 

 According to Yegunov and Vinogradski, there is at this 

 depth a race of sulphur bacteria which derive the energy 

 necessary for their existence from the sulphur of the sulphu- 

 retted hydrogen. The sulphuretted hydrogen is separated in 

 their cells in the form of soft, oily globules and the oxidation 

 of this sulphur gives them the necessary vital energy in 

 precisely the same manner as the oxidation of carbon in other 

 organisms supplies it. I must express my indebtedness to 

 the presidential address to the Geological Society by Dr. Teall 

 for the above facts, especially as it has led to the train of 

 reasoning adopted in the present article. 1 



The organic substance of plants and animals, the protoplasm, 

 consists essentially of carbon, hydrogen, oxygen, nitrogen, 

 sulphur and phosphorus. We have dealt with the separation 

 of all these by micro-organisms except the last. We know of no 

 phosphorus-eating bacteria but phosphorus exists plentifully 

 in the soil, being derived from the mineral apatite, a calcium 

 phosphate, which is an accessory mineral in all igneous 

 rocks. The natural phosphates of lime and magnesia are 

 readily soluble in all weak acids and are available directly 

 to the plant roots ; but if there is any hydrated oxide of 

 iron present in the soil, there is formed a phosphate of iron 

 which is totally insoluble. Basic slag, for instance, which 

 contains large quantities of phosphorus and iron, lies unaltered 

 on fields with damp soil showing an acid reaction. As 

 previously stated, Kunze has proved that in many of the higher 

 plants the roots do not secrete organic acids, the only secretion 

 being water containing carbon dioxide. Prianischnikoff found 

 that on growing peas, lupines, mustard and buckwheat, in sand 

 containing aluminium phosphate, which, like phosphate of iron, 

 is insoluble in carbonic acid, there was a vigorous absorption 

 of the phosphates by the plants and the conclusion he arrived 

 at was that the breaking down of the insoluble substance had 

 been accomplished by bacteria. 2 



In South Africa the central parts of the country are dry ; 

 along the river courses there are magnificent stretches of 

 alluvium, which, however, can only be occasionally watered 

 by floods or artificial irrigation. The soil is usually rich in 



1 J.' J. H. Teall, Quart. Journ. Geol. Soc. vol. lviii. p. lxvii. 



2 D. Prianischnikoff, Bericht. deutsch.bot. Ces. vol. xxii. 1904, p. 184. 



