250 HOW CKOPS GKOW. 



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. 110. 



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 microscope. According to this ob- 

 server, the cell-contents of the seed (cotyledons) of the 

 common nasturtium {Tropwolum majus) run through 

 the following metamorphoses. Up to a certain stage in 

 its development the interior of the celj^ 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. Ata 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 

 lose their green color and assume, both as regards appear- 

 ance and deportment with iodine, all the characters of 

 starch. Subsequently, as the seed hardens and becomes 

 firmer in its tissues, the microscope shows 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 converted into cellu- 

 lose or bodies of similar properties. Again, later, the nu- 

 cleus, 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 starch-grains are gradually converted 



