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 
ig 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 lhe near the nucleus of 
the cell. Like the other plastids, they consist of a spongy 
