i 5 2 SCIENCE PROGRESS 



the pavements of Berlin there were still considerable numbers 

 at a depth of eight to ten feet. 1 



Bacteria predominate in cultivated lands, whilst moulds are 

 found in open meadow and in fresh soil. It is a function of the 

 moulds to keep the surface layer open ; they send their hyphae 

 between the grains of sand and particles of clay, push them 

 aside and make channels for the entrance of air. They may be 

 called Nature's tillers. In cultivated ground man ploughs and 

 harrows the land so that an artificial tilth is produced far in 

 excess of that in natural soil and crops grown on it are 

 enabled to thrive without hindrance ; whereas if the same seed 

 were planted in natural soil, just sufficiently aerated to support 

 the indigenous flora, the germinating plants would be stifled. 



The work of the moulds in another direction can be seen 

 on pine-needle litter or fresh leaf litter, where the leaves are 

 bound together by a web made of the tender filaments of 

 growing moulds and decomposition goes on rapidly. Rostrup 2 

 called this particular form of mould Clodosporium humifaciens 

 but there are doubtless many kinds at work, all active in 

 breaking down the cellulose of plants into humus. It is this 

 parasitic and saprophytic action of the lower organisms that 

 has overshadowed the importance of their other less obvious 

 activities. Many species are certainly specially fitted to 

 promote fermentation, putrefaction, decay in all its forms in 

 vegetable and animal tissues but some have other work to 

 do. Kunze has shown that the higher plants have roots that 

 are incapable of breaking down the mineral substances which 

 they absorb and Kunze attributes the assimilation of these 

 to the work of bacteria and moulds. 3 Nikitinsky, 4 Czapek and 

 Kohn 6 have shown that cultures of the moulds Aspergillus 

 mger and Penicillium glaucum, when fed with ammonium 

 chloride, set free hydrochloric acid, which alone or in the 

 presence of nitrates is capable of dissolving most of the known 

 mineral substances. It is not impossible, therefore, as has 

 been assumed, that the precipitation of gold in the hot water 

 of the Steamboat Springs of Nevada is brought about by the 



1 Fraenckel, Zeitschr. f. Hygiene, vol. ii. p. 521. 



2 E. Ramann, loc. cit. p. 119. 



3 G. Kunze, Jahrbiich, iviss. Bot. vol. xlii. 1906, p. 357. 



4 J. Nikitinsky, Jahrbikh, wiss. Bot. vol. xl. 1904, p. 1. 



5 F. Czapek and E. Kohn, Hofmeist. Beitriige z. C/iein. Phys. vol. vii. 1906, 

 p. 302 ; F. Czapek, Progressus rei botanicce, Jena, 1907, p. 436. 



