Scientific Agriculture. 



526 



[December, 1009. 



and so on. The following estimates are 

 given by Ramann of the relative pro- 

 portions in the various types of soil* :— 



Type of soil, 



Bacteria 

 in 1 grm. of 

 dry substance. 



35,000,000 



1,647,000 

 31,000,000 



264,000 



40,000,000 

 50,000,000 

 4,860,000 

 2,500,000 

 247, 000 



Fungi 

 in 1 grm. of 

 dry substance. 



60,000 



343,000 

 560,000 



800,000 



3,430,000 

 Uncountable 

 4,000-277,000a 

 66, 000-566, 000a 

 35,000-350,000« 



1. Pines with beech 



undergrowth 



2. Pines in boggy 



ground 



3. Beech-leaf mould 



4. Old leaf mould 



below No. 3 



5. Leaf mould in oak 



coppice 



6. Pine-needle mould 



7. Loamy soil 



8. Sandy soil 



9. Soil below humus 



These numbers may seem enormous, 

 but it must be remembered that the bac- 

 teria and spores are very small : a bac- 

 terium is about one-thousandth of a milli- 

 metre in diameter, and the "saturation" 

 point in soil is only reached when there 

 are six hundred million bacteria in a 

 cubic centimetre. 



The manner of estimating such germs 

 is by growing cultures in nutrient gela- 

 tine and agar-agar, and then counting 

 the developing colonies of bacteria ; the 

 results are approximate only, and there 

 are doubtless many that do not germi- 

 nate in the particular medium employed. 

 Others again are too small to be recog- 

 nised under the highest powers of the 

 microscope. Another factor which in- 

 creases the difficulties of estimation is 

 the enormous powers of multiplication 

 which these organisms possess : a bac- 

 terium divides into two every thirty-five 

 minutes ; one bacterium, therefore, at 

 the end of twelve hours will have four 

 million descendants, so that the numbers 

 in the soil vary from moment to moment. 



Whilst actual numbers cannot be 

 given definitely, the proportions are 

 more or less correct. It has been found 

 that bacteria are more abundant in 

 the first foot of soil.t Thus Adametz 

 found in one gramme at the surface 

 38,000 bacteria, whilst at a depth of ten 

 inches there were 460,000. In this parti- 

 cular sample there were only 40 to 50 

 fungus germs, of which six species were 

 true moulds and four were ferments, 

 including the yeasts of wine and beer. 

 At three feet down the numbers decrease 

 rapidly in proportion to the aeration of 

 the soil. Fraenckel, however, found 

 that even in the soil beneath the pave- 

 ment of Berlin there were still consider- 



* E. Ramann, Bodekunde, Berlin, 1909, p, 120. 

 f Adametz, Inaug. Diss. Leipzig, 1876. 

 a From one cubic centimetre. 



able numbers at a depth of eight to ten 

 feet.* 



Bacteria predominate in cultivated 

 lands, whilst moulds are found in open 

 meadow and in fresh soil. It is a func- 

 tion of the moulds to keep the surface 

 layer open ; they send their hyphse 

 between the grains of sand and parti- 

 cles of clay, push them aside and make 

 channels for the entrance of air. They 

 may be called Nature's tillers. In culti- 

 vated 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 ate unable 

 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 works 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 by the tender filaments of growing 

 moulds and decomposition goes on 

 rapidly. Rostrupt called this particular 

 form of mould ClodospoHumhumifaciens, 

 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 over- 

 shadowed 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 assimi- 

 lation of these to the work of bacteria 

 and moulds.J Nikitinsky,§ Czapek and 

 Kohn|| have shown that cultures of the 

 moulds Aspet gillus niger and Penicillium 

 glacum, when fed with ammonium chlo- 

 ride, 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 Spring of Nevada 

 is brought about by the action of 



* Fraenckel, Zeitschr; f. Hygiene, Vol. ii. 

 p, 521. 



f B. Ramann, loc. cit. p. 119, 



X G, Kunze, Jahrbuch, tviss. Bot. Vol. xlii. 

 1906, p. 357. 



§ J. Nikitinsky, Jahrbuch, wiss. Bot. Vol. xl. 

 1904. p. 1. 



|| F; Czapek and E, Kohn, Hofmeist. Beitrage 

 :.. Chem. Pliys. Vol. vii. 1906, p. 302 ; F. Czapek, 

 Progrcssus rcibotanicoc, Jena, 1907, p. 436. 



