132 THE MECHANISM OF ABSORPTION AND TRANSLOCATION 



bi-carbonate is absorbed by a green plant, the chalk forms an extracellular 

 deposit while the liberated carbon dioxide is assimilated. Similarly sodium 

 bi-carbonate (NaHCO ;; ) may lose when presented to the plant as much 

 as 70 per cent, of its carbonic acid. The sodium carbonate produced 

 (Na 2 CO s ) docs not penetrate within the cells, but remains in the external 

 fluid which it turns markedly alkaline 1 . 



Alkaline and acid reactions may be produced by substances directly 

 excreted by the plant. Thus fungi may form and excrete acids or 

 ammonia when fed solely upon proteids (Chap. VIII). A few phanerogams 

 evolve trimethylamine, while Char a and certain algae give off alkaline 

 secretions in pure water, which may be detected by the colour-reaction of 

 phenolpthalein, or by the decomposition of Prussian-blue previously de- 

 posited upon the cell-wall 2 . It is hence not surprising that in water-cultures 

 of phanerogams the fluid may either become alkaline 3 , or acid, according 

 to its composition. In certain researches by Rautenberg and Kuhn 4 , the 

 presence of a large amount of ammonium chloride caused so marked 

 a production of acid that maize and kidney-bean seedlings soon died. 

 Moreover, according to Biedermann, when seeds swell in neutral solutions 

 of chlorides of the alkalies or alkaline earths, the external fluid becomes 

 alkaline, while according to Knop, when the seeds are in water containing 

 calcium sulphate, the calcium of the salt is absorbed in somewhat greater 

 amount than is the acid 5 . 



Calcareous Incrustations. The excretion of chalk by the plant may take 

 place in a variety of ways. Hence the incrustations found especially well marked 

 on certain fresh-water and marine algae, and upon leaves and stems of Pota- 

 mogeton and other water plants, as well as on fungi and the roots of land plants, 

 need not necessarily have the same origin 6 . In many mosses (Eucladium verti- 

 dllatum, Trichostomum tophaceum, &c.) growing in water rich in bi-carbonate of 

 lime, the incrustation is formed but little more actively than it is on dead objects, 

 the living plant hence playing an almost passive part 7 . The incrustations on algae 

 are apparently mainly due to the activity of the plant itself, for under similar 



1 Hassak, Unters. a. d. Bot. Inst. z. Tubingen, 1888, Bd. ir, p. 471. 



3 Klebs, Unters. a. d. Tot. Inst. z. Tiibingen, 1886, Bd. II, p. 340; Hassak, ibid., p. 476. 



3 Knop, Ann. d. Chem. u. Pharm., 1862, Bd. cxxi, p. 313. On alkalinity in sand cultures, 

 see Boussingault, Agron., Chim. agr.,&c., 1860, T. i, pp. 273, 279; Stutzer, Versuchsst, 1878, Bd. xxi, 

 p. in. It is not impossible that here bacterial activity may produce the results observed. 



4 Rautenberg und Kuhn, Versuchsst., 1864, Bd. vi, p. 358. Cf. Dworzak uncl Knop, Ber. d. 

 Sachs. Ges. d. \Viss., Leipzig, 1875, i, p. 74; Wagner, Versuchsst., 1871, Bd. xin, p. 221. Under 

 different conditions, Czapek (Jahrbuch. f. wiss. Bot., 1896, Bd. xxix, p. 23) found no secretion of 

 acid to be caused by the presence of sal-ammoniac, nor does it necessarily follow that the roots of all 

 plants will have this power. See Sect. 28. 



5 Biedermann, Versuchsst., 1867, Bd. ix, p. 312 ; Knop, Versuchsst, 1864, Bd. VI, p. Si. 



c For literature see Kohl, Kalksalze u. Kieselsaure in cler Pflanze, 1889, p. 99. Of more recent 

 researches cf. Cramer, Uber die verticillirten Siphoneen Neomeris u. Bornetella, 1890, p. 9; [Church, 

 Annals of Botany, vol. ix, 1895, p. 602]. With the chalk, calcium oxalate &c. may be associated. 



7 Cf. Unger, Ber. d. Wien. Akad., 1861, ii, p. 509. 



