ELEMENTS OF ORGANIC STRUCTURE. 225 
ones, mosi of them, are occupied entirely with starch, fig. 
52, p. 277. In oats, wheat, and other cereals, we find, just 
within the empty cells of the skin or epidermis of the 
grain, a few layers of cells that contain scarcely anything 
but albuminoids, with a little fat; while the interior cells 
are chiefly filled with starch; fig. 18, p. 106. 
Transformations in Cell Contents.—The same cell may 
exhibit a great variety of aspect and contents at different 
periods of growth. This is especially to be observed in 
the seed while developing on the mother plant. Hartig 
has traced these changes in numerous plants under the mi- 
croscope. According to this observer, the cell-contents of 
the seed (cotyledons) of the common nasturtium, (Z7rop- 
golum majus,) run through the following metamorphoses. 
Up to a certain stage in its development the interior of 
the cells are nearly devoid of recognizable solid matters, 
other than the nucleus and the adhering protoplasm. 
Shortly, as the growth of the seed advances, green grains 
of chlorophyll make their appearance upon the nucleus, 
completely covering it from view. At a later stage, these 
grains, which have enlarged and multiplied, are seen to 
have mostly become detached from the nucleus, and lie 
near to and in contact with the cell-wall. Again, in a 
short time the grains have lost their green color and have 
assumed, both as regards appearance and deportment with 
iodine, all the characters of starch. Subsequently, as the 
seed hardens and, becomes firmer in its tissues, the micro- 
scope reveals that the starch-grains, which were situated 
near the cell-wall, have vanished, while the cell-wall itself 
has thickened inwardly—the starch having been converte 
ed into cellulose, Again, later, the nucleus, about which, 
in the meantime, more starch-grains have been formed, 
undergoes a change and disappears ; then the starch-grains, 
some of which have enlarged while others have vanished, 
are found to be imbedded in a pasty matter, which has the 
reactions of an albuminoid. From this time on, the 
