ioo THE MECHANISM OF ABSORPTION AND TRANSLOCATION 



According to Czapek the roots of Phanerogams generally excrete small traces 

 of substances, one of which is acid potassium phosphate \ but since the amount 

 excreted is extremely small, it is not surprising that macrochemical investigations 

 have frequently yielded negative results 2 . The older positive results are for the 

 most part indecisive, since sufficient precautions were not taken to ensure that the 

 excreted substances were not derived from dead or dying cells, as was probably 

 the case with regard to the sugar found by Boussingault and Detmer (1. c.) in the 

 water in which fruits had lain. 



Fats. The results obtained by R. H. Schmidt 3 establish the fact that fatty 

 substances, and especially fluid fatty acids, can penetrate the living cell with 

 comparative ease. The presence of only a minute amount of a fatty acid renders 

 possible a fairly rapid absorption of neutral oil, such as olive oil, which the 

 cell normally absorbs only slowly and in trifling amount. To demonstrate the 

 absorption of fat, a strip of filter paper impregnated with the fatty substance may 

 be inserted in a longitudinal incision of about i cm. length made in the young 

 etiolated stem of a seedling of Pisum satirum. If the fat has been coloured with 

 alkanna, it can be traced into the intercellular spaces, and after a few hours per- 

 ceptible absorption has occurred, leading in one to two days to a marked accu- 

 mulation within the neighbouring cells. At first the fat is present in the plasma 

 in so fine a state of division, that in some cases it only becomes visible when 

 the action of reagents causes the minute droplets to coalesce with one another. 

 This takes place normally, as a general rule, as the quantity present increases, 

 and later still, fat globules appear to a greater or less extent in the cell-sap. 



The fat is apparently absorbed as such, and hence it is probable that oils also 

 are directly transferred from cell to cell. The appearance and accumulation of 

 fatty material follow the same course in nature, for when fat undergoes trans- 

 location, free fatty acids appear to be always present (Sect. 82). Even plants 

 which are normally poor in oily substances have also the power of absorbing fat, 

 while those fungi, which may be nourished by neutral fats, must apparently be able 

 to split the fat into the fatty acid and glycerine of which it is composed. Fungal 

 hyphae, growing on solid cacao-butter, absorb and extract nutriment from it, and 

 the protoplasts of higher plants can absorb it when the temperature is high enough 

 (30 C) to keep it in a fluid condition. 



The means by which the particles of oily substance are enabled to penetrate 

 the cell-wall saturated with water, and to pass through it, as well as through the 

 plasmatic membranes, have not yet been determined. Oil is, however, able to pass 

 in the form of a fine emulsion through animal membranes impregnated with soap 

 or bile, and probably in plants also the process is one of emulsification. Dead 



1 Czapek, Jahrb. f. wiss. Bot., 1896, Bd. XXIX, p. 321. 



2 Lit.: Hofmeister, Pflanzenzelle, 1867, p. 4; J. Boussingault, Agron., Chim. agric. etPhysiol., 

 1874, vol. v, p. 309; Pfeffer, Landw. Jahrb., 1876, Bd. v, p. 125; Schulze und Umlauft, I.e., 1876, 

 Bd. V, p. 828; Detmer, Forsch. a. d. Geb. d. Agriculturphysik, 1879, Bd. II, p. 372; van Tieghem 

 et Bonnier, Bull. d. 1. Soc. Bot. d. France, 1880, vol. xxvii, p. 1 16. 



8 R. H. Schmidt, Flora, 1891, p. 300. See Pfeffer, Aufnahme u. Ausgabe ungelb'ster Korper, 

 1890, p. 179. The literature is quoted in these works. 



