CARBOHYDRATES AND FATS 479 



seeds, but also in many tubers, trees, trunks, &C. 1 Along with the neutral fats 

 a slight amount of fatty acid may occur, or none may be present. During trans- 

 location the amount of free fatty acid increases to such an extent that as much 

 as 10-30 per cent., or even almost the whole of the fatty acid may be liberated 2 . 

 In addition to oleic, palmitic, and stearic acids, a few of the higher acids may 

 be present either singly or more usually several together, and either as such or as 

 glycerides. As a general rule the fluid fats (oils) are more abundant, but the seeds 

 of Cocoa and of Myrisiica contain fats which even in the living cells remain solid at 

 ordinary temperatures 3 . 



Apparently no special oil-forming plastids exist, the fats appearing directly 

 in the protoplasm in a fine state of sub-division, and running together to form 

 drops as the amount present increases. These drops are then excreted into the 

 cell-sap, and the same occurs when fat is absorbed from without 4 . In seeds 

 the main mass of the oil present is found in the vacuoles mingled with the 

 aleurone grains, &c. 



During germination any oil present is re-emulsified 5 and absorbed anew 

 by the protoplasm in order that it may undergo further change. The separation 

 of neutral fats into fatty acids and glycerine may, however, take place in the cell-sap, 

 and fungi are able to induce an extracellular decomposition of fats, while they can 

 assimilate solid fats if these are only in a sufficiently finely divided condition. 

 To what extent these powers are due to the formation and excretion of enzymes is 

 unknown (Sect. 91). Even when the liberation of fatty acids is most active no 

 glycerine can be detected, so that it is evident the latter must be very rapidly 

 assimilated. The absorption and translocation of fats are markedly aided by the 

 presence of free fatty acids (Sect. 16). 



On the increased absorption of oxygen necessitated when fats are being 

 consumed, see Sect. 96. Waxy substances are mainly aplastic and usually 

 accumulate in the substance or surface of the cell-walls 6 . 



Lecithins are fatty substances or glycerides which contain, in addition to 

 fatty acids, cholin and esters of phosphoric acid. Lecithin may form an essential 

 constituent of protoplasm (Sect, n), but whether lecithins take part in the 



1 On the production of fat by CO 2 -assimilation, cf. Sect. 54. The aplastic waxy substances and 

 the occurrence of aplastic fat-masses have already been mentioned. 



" R. H. Schmidt, Flora, 1891, p. 345 ; Mtintz, Ann. d. chim. et d. phys., 1871, iv. sen, T. xxir, 

 p. 472, and in Boussingault's Agron., Chim. agric., &c., 1874, T. V, p. 50; Mesnard, Annal. d. sci. 

 nat., 1893, vii. sen, T. xvin, p. 298. 



3 Pfeffer, Jahrb. f. wiss. Bot., 1872, Bd. VIII, p. 485; 



1 Cf. R. H. Schmidt, 1. c., pp. 325, 338 ; Pfeffer, Aufnahme u. Ausgabe ungeloster Korper, 1890, 

 p. 180. Chromatophores are able to produce oil, and it is possible that the latter may in some cases 

 be mainly formed by special plasmatic organs, or may accumulate in them. On Elaioplasts (oil- 

 formers), see the literature given by Zimmermann, Beih. z. Bot. Centralbl., 1894, Bd. iv, p. 165; 

 v. Kiister, Oelkorper d. Lebermoose, 1894; Schiitt, Die Peridineen, 1895, p. 75. Altmann's sup- 

 position that the plasmatic granules (microsomala) are special oil-forming organs can hardly be 

 correct. 



5 Pfeffer, Jahrb. f. wiss. Bot., 1872, Bd. vm, p. 525. 



* Cf. de Bary, Vergl. Anat., 1877, p. 86; Haberlandt, Physiol. Pflanzenanat., 1896, 2. Aufl., 

 p. 96. See also Sect. 21. 



