IMPORTANCE AND PROPERTIES OF THE SOIL 



173 



The absence of any solvent action upon plates of aluminium phosphate shows 

 that at no period of its development are any strong fixed acids excreted by 

 the root, nor can any free hydrochloric acid be formed by the interaction of the 

 monopotassium phosphate with metallic chlorides 1 . Similarly the carbonic acid 

 excreted by the roots is unable to liberate any free acid from chlorides, nitrates, 

 sulphates, &c., for were only a trace set free, as this was repeatedly fixed and 

 removed, the continuance of the process would finally lead to a marked result 

 (cf. Sect. 22). An example of such action is afforded by oxalic acid and by the 

 weaker tartaric acid as well, for if sodium chloride or potassium nitrate are 

 added to solutions of these acids, they attack pieces of marble more energetically 

 than they did before 2 . Actions of this character assuredly occur in nature, when, 

 as in fungi , organic acids are excreted, and at the same time the other necessary 

 conditions are fulfilled. With or without such aid, fungi exert very pronounced 

 solvent actions by the aid of acid secretions, as, for example, when lichens eat into 

 the rocks on which they grow 3 . It is not yet 

 precisely determined whether those algae, which 

 can bore into chalky rocks, do so by means of 

 the excretion of carbonic acid, or of other acids 

 also*. It is moreover possible, though details 

 cannot be given here, that organisms can at the 

 same time form chalky deposits, and dissolve 

 chalky rocks ; so that it is not surprising that, ac- 

 cording to Rosen B , a plasmodium of Aethalium 

 septicum, although it contains chalk, may corrode 

 a marble plate. 



Since fungi excrete acids under special 

 cultural and nutritive conditions, while under 

 different circumstances they produce alkalies, 

 it appears possible that higher plants may, under 



special conditions, be able to excrete free acids other than carbonic acid. A few 

 observations already mentioned (Sect. 22) do indeed favour this conclusion, while 

 it must not be forgotten that a production of acid may, as is the case in fungi, take 

 place in a regulatory manner, in correspondence with the demands made upon the 

 organism. A variety of different acids may be excreted by fungi. According to 





FIG. 1 8. The glass cylinder (a) is covered 

 with parchment (c) and is filled with very 

 dilute hydrochloric acid, as is also the outer 

 vessel (b). If pieces of marble are placed on c, 

 in an hour or so the presence of calcium in 

 the outer fluid may be demonstrated by the 

 addition of oxalic acid and ammonia. (.Opti- 

 cal section, one-fifth natural size.) 



1 Maby, Chem. Centralbl., 1878, p. 56 ; Czapek, Jahrb. f. wiss. Bot., 1896, Bd. xxix, p. 365- 



Emmerling, Ber. d. Chem. Ges., 1877, Bd. x, p. 650 ; Versuchsst., 1884, Bd. xxx, p. 109. This 

 results from the respective affinities of the different acids present, on which see L. Meyer, Die mod. 

 Theorien d. Chem., 1884, 5. Aufl., p. 482, and Sect. 22. On the proofs of the presence of free F Cl, 

 &c. in such cases, see Salkowski, Ber. d. Chem. Ges., Ref. 1892, p. 343! Detmer, Bot. Zeitung, 



884 3 Bachmann, Ber. d. Bot. Ges., 1890, p. 141 ; 1892, P- 35 J FiinfstUck, Beitrage z. wiss. Bot., 1895, 

 Bd. I p. 157. On fungi, cf. Zopf, Die Pilze, 1890, p. 185. That by means of this acid-secretion, 

 fungi'can bore rapidly through plates of chalk to which they are chemotactically attracted has b( 

 shown by Lind's researches carried out in the Bot. Inst., Leipzig. 



* Cohn, Jahresb. d. Schles. Ges. f. vaterl. Cultur, 1893, p. 19, and the literature there cited ; also 

 C. Schroter u. O. Kirchner, Vegetation des Bodensees, 1897. 



8 Quoted by Cohn, I.e.. p. 22. 



