ORGANIZED CELL-CONTENTS. 
11 
appearances are observed, which, however, may be due 
to postmortem changes. 
NUCLEUS. 
In the protoplasm of mature and active cells there is 
usually present a differentiated body, already referred 
to, which is known as the nucleus. It is a more or 
less spherical, ovoid, or narrow ellipsoidal body, consist- 
ing of a somewhat fibrous and granular substance, 
which is imbedded in a ground substance, the whole 
being surrounded by a membrane-like portion. While 
closely resembling the protoplasm, it may be differ- 
entiated by staining with iodine, borax-carmine or 
methylene green in acetic aid. 
PLASTIDS. 
The plastids, or chromatophores, are also differen- 
tiated bodies found in the protoplasm, and which are 
associated with it in the building up of complex 
organic compounds. They are found in all plants, 
with the exception of the fungi, and possibly some of 
the lower forms of algse. According to the position of 
the cells in which they occur and the functions they 
are to perform, they vary in color — three distinct kinds 
being recognized. In the egg-cell and in the cells of 
roots, rhizomes, and seeds, the plastids are colorless and 
are called leucoplastids. When contained in cells which 
are more or less exposed to the light, they are known 
as chloroplastids, or chlorophyl grains. In other cases, 
independently of the position of the cells as to light or 
darkness, they may develop a yellowish or orange-col- 
ored principle, and are then known as chromoplastids. 
The plastids consist of a protoplasmic-like substance, 
and vary in form from more or less spherical to polyg- 
onal or irregular-shaped bodies. They suffer decom- 
position much more readily than the nucleus, and are 
