ELEMENTS OF ORGANIC STRUCTURE. 229 



ones, most 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, (Trop- 

 ceolum 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 convert- 

 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 



