246 VEGETABLE PHYSIOLOGY 



strictly connected with the mechanisms of dispersion of 

 seeds. 



The mode of deposition of oil or fat is not at all well 

 known. It is generally found saturating the protoplasm of 

 the cell in which it lies, and not occupying a definite space 

 as do aleurone and starch grains. Whether it is secreted 

 from the substance of the protoplasm, or whether the 

 materials of which it is made are taken to the latter in a 

 state near the condition of the finished fat, is uncertain. It 

 is formed by the combination of a fatty acid with gly- 

 cerine. Both these bodies can be formed in the plant, but 

 how they are finally presented to us in the shape of oil is 

 still in need of elucidation. As the oil appears in the cell 

 it seems to point to a process of breaking down of the 

 protoplasm itself, and not to a direct combination of the 

 antecedents mentioned. If we stain cells which are forming 

 fat with osmic acid, which colours fatty bodies brown or 

 black, we see in the protoplasm small specks of fatty 

 matter, which, while in the youngest cells mere dots, are 

 in older ones larger, and can be recognised as droplets. In 

 still older ones the blackness permeates the whole proto- 

 plasm, indicating that the latter is saturated with the oil, 

 the droplets having run together in consequence of their 

 number and dimensions. 



The appearances are, however, not inconsistent with the 

 view that the work of the protoplasm is only to effect 

 the ultimate changes, or interaction of the glycerine and 

 the fatty acids, which are transported separately to the cells 

 or perhaps formed there from some antecedent. 



The deposition of fat in some cases, particularly in 

 leaves, has been stated to be effected by the agency of certain 

 plastids corresponding to the leucoplasts already mentioned 

 in connection with the formation of starch grains. These 

 structures, which have been called elaioplasts, are curious 

 bodies of various shapes, sometimes round or oval, some- 

 times irregular in contour, which lie near the nucleus of 

 the cell. Like the other plastids, they consist of a spongy 



