ABSORPTION OF MATERIALS IN GENERAL 



115 



The moulds Aspergillus niger and Penicillium glaucum may develop osmotic 

 pressures as great as 157 atmospheres, when they are grown in concentrated 

 sugar or salt sqlutions." 



DeVries determined the partial osmotic pressures developed by some of the 

 constituents of the cell sap. The following table gives an idea as to what sub- 

 stances are instrumental in the production of osmotic pressure in plants. The 

 figures denote percentage of the total pressure. 



Diffusion in solution is very important in the absorption of materials by 

 plants but it cannot account for the transfer of absorbed substances within the 

 plant, for movement by diffusion alone is much too slow.^ For example, it 

 would take 319 days for i mg. of sodium chloride, a rapidly diffusing substance, 

 to diffuse I m. out of a 10 per cent, solution of that salt. A period of fourteen 

 years would be required for the same amount of albumin to migrate the same dis- 



1 Stefan, J., tJeber die Diffusion der Flussigkeiten. II. Berechnung der Grahamschen Versuche. 

 Sitzungsber. (matA.-naturw. Kl.) K. Akad. Wiss. Wien 79-^^: 161-214. 1879. Vries, Hugo de, Ueber die 

 Bedeutung der Circulation und der Rotation des Protoplasma fiir den Stofftransport in der Pflanze. Bot. 

 Zeitg. 43: 1-6,17-26. i88s. 



» Fitting has studied the osmotic pressures of the cells of plant leaves, by the plasmolytic 

 method, using potassium nitrate solutions, in a very thorough way. He dealt especially with 

 desert plants. See: Fitting, Hans, Die Wasserversorgung und die osmotischen Druckver- 

 haltnisse der Wustenpflanzen. Zeitsch. Bot. 3 : 209-275. 1911. Livingston, B. E., The rela- 

 tion of the osmotic pressure of the cell sap in plants to arid habitats. Plant world 14 : 153-164. 

 1911. (This is a somewhat critical review of Fitting's paper.) While plant cells in general 

 have osmotic pressures of from 5 to 11 atmospheres, Fitting found pressures much exceeding 

 100 atmospheres in the leaves of some desert plants. This value is greater for plants growing in 

 very dry habitats than for those growing in more moist situations. For further studies bearing 

 on this and related matters, see: Dixon, H. H., and Atkins, W. R. G., On osmotic pressures in 

 plants and on a thermo-electric method of determining freezing points. Proc. Roy. Dublin 

 Soc, n.s. 12 : 275-311. 1910. Idem, Osmotic pressures in plants. I. Methods of extracting 

 sap from plant organs, /fiid. n.s 13 : 422-433. 1913. (Reprinted in: Notes from Bot. Sch., 

 Trinity Coll., Dublin 2: 154-165. 1913.) Idem, same title, II. Cryoscopic and conductivity 

 measurements on some vegetable saps. Ibid. n.s. 13 : 434-440. 1913. (Reprinted in: Notes 

 from Bot. Sch., Trinity Coll., Dublin 2 : 166-172. i9»3.) Harris, J. Arthur, andLawrence, 

 John v., assisted by Gortner, R. A., The cryoscopic constants of expressed vegetable saps 

 as related to local environmental conditions in the Arizona deserts. Physiol res. 2 : 1-49. 

 1916. (Other papers are there referred to.) Hibbard, R. P., and Harrmgtonj O. E., De- 

 pression of the freezing-point in triturated plant tissues and the magnitude of this de- 

 pression as related to soil moisture. Ibid. 1: 441-454.. 1916. For a general discussion of 

 the osmotic relations of cells see: Atkins, W. R. G., Soma rec ent researches in plant 

 physiology. xi-H328 p. London, igi6. — 'Ed. 



