THE VEGETABLE CELL. 
385 
blue colour, the nucleus and the rest of the protoplasm retaining 
a brownish yellow tint. The exact part played by the nucleus 
in the functions and in the multiplication of cells is a point at 
present involved in much obscurity. Protoplasm differs in its 
chemical composition from cellulose in containing nitrogen ; 
but the experiments hitherto made have failed in assigning to 
it any definite and constant formula. 
In addition to water and protoplasm, which are contained in 
every cell when in a growing condition, other substances are 
frequently or generally present, of which some of the most 
important may here be mentioned. 
Starch is the first product of assimilation, that is, of the 
Fig. 2. 
Starch-grains from a potato-tuber ( x 800). A, an older simple 
grain; B, a partially compound grain ; C, D, perfectly compound 
grains ; E, an older grain, the nucleus of which has divided ; a, 
a very young grain ; b, an older grain ; c, a still older grain 
with divided nucleus. 
union of the elements of water absorbed by the root with the 
carbon removed by the leaves from the carbonic acid of the 
atmosphere. Its chemical composition is identical with that 
of cellulose, but its properties are different. It never enters, 
moreover, into the constitution of the cell-wall, but is always 
VOL. XIII. — NO. LIII. C C 
