219 



Not only upon the surface of exposed rocks have these organisms 

 been discovered, but also to a considerable distance in the interior of 

 rocks on high mountains, fragments of which have been collected in 

 sterilised tubes and subjected to cultivation in an appropriate environ- 

 ment. 



DECAY OF ROCKS AT HIGH ALTITUDES. 



The naked rocks of high mountains comprise mineralogical types of 

 the most varied nature, viz , granite porphyry, gneiss, mica schist, vol- 

 canic rocks and limestones of all varieties, and all these have been found 

 to be covered with the nitrifying ferment which is doubtless extremely 

 active in producing incipient decay. At the high altitudes at which, 

 these observations have been made the activity of bacteria is necessarily 

 limited by the low temperature to which they are subjected the greater 

 part of the year. During the winter season their life is suspended, but 

 is not extinguished since they have been found living and ready to re- 

 sume all their activity after an indefinite sleep, perhaps of thousands of 

 years, on the ice of the glaciers, where the temperature never rises above 

 the freezing point. When the activity of these ferments in the most 

 unfavourable conditions is recognised, it is easily seen how much more 

 active they become when brought down to lower levels where they are 

 nourished by the favouring conditions which exist, especially during the 

 summer time, in cultivated soils. In fact, the importance of the action 

 of these bodies on the mineral particles of which the soil is largely com- 

 posed has never been fully recognised, and there is no doubt whatever 

 of the great significance of their decomposing action in the liberation of 

 plant food locked up in undecomposed mineral structures In this case 

 the activity of the bacteria is not limited to the surface of rock masses, 

 but permeates every particle of soil and thus becomes effective over a 

 vastly extended surface. 



When the extreme minuteness of these organisms and the phenomena 

 which they produce is considered there may be a tendency to despise 

 their importance, but by reason of the fact that their activity is never- 

 ceasing and of the widest application, it must be placed among the 

 geological causes to which the crust of the earth owes a part of its actual 

 physiognomy and to which the formation of the deposits of the com- 

 minuted elements constituting arable soil are due. 



TRANSLATION OF MINERAL MATTERS IN PLANTS. 



Consider for a moment a minute fragment of mineral matter of any 

 description containing particles of plant food presented to the rootlet of 

 a plant. It is evident at once that no mineral particle, however minute, 

 can be bodily transported in a mechanical way and become an integral 

 part of any plant tissue. Any attempt to move soil particles in this 

 manner could only result in a clogging of the pores of the cellular tis- 

 sues, the stoppage of the circulation, and consequent death of the plant. 

 The mineral particles in question, therefore, must suffer a complete dis- 

 integration, and the only forces capable of affecting this, in so far as we 

 know, are the solvent action of the plant secretions, the vital activity of 

 the rootlet itself and the decomposing influence of the soil ferments. 

 What particular proportion of the solvent action is due to each of these 

 causes has not yet been determined. It is known, however, that the 



