18 PHARMACEUTICAL BOTANY 
A Typicat Co.torLess PLANT CELL 
If we peel off a portion of the thin colorless skin or epidermis 
from the inner concave surface of an onion bulb scale, mount in 
water and examine under the microscope, we find it to be com- 
posed of a large number of similar cells which are separated from 
one another by means of lines, the bounding cell walls. Under 
high power each of these cells will exhibit the following 
characteristics: 
An outer wall, highly refractile in nature and composed of 
cellulose which surrounds the living matter or protoplasm (see Fig. 
10). This wall is not living itself but is formed by the living 
matter within the cell. It is sufficiently rigid to give definite 
shape to the cell and sufficiently porous to allow water with sub- 
stances in solution to pass through it. Somewhere within the 
protoplasm will be noted a denser-looking body. ‘This is the 
nucleus. The nucleus is called ‘“‘the superintendent | of the cell” 
since it is believed to control all the activities of the protoplast. 
Its removal results in the death of the cell. It is usually spherical 
in shape but in old “epidermal cells of the onion becomes some- 
what flattened and pushed up against the outer plasma membrane 
and cell wall. It is surrounded by a nuclear membrane and con- 
tains a nuclear reticulum, nuclear sap and one or more nucleoli. 
The nuclear reticulum can best be seen after the cells are fixed 
and stained. It consists of a thread-like net of a colorless sub- 
stance called linin adhering to which are granules of a substance 
which takes the stain of a basic dye called chromatin. Chromatin 
carries the genes or hereditary characters from parent to offspring. 
The nuclear-sap is a watery solution of nourishing substances. 
Within the nucleus will be seen one or more smaller highly 
refractile and definitely circumscribed, dense protoplasmic bodies, 
the nucleolus or nucleoli. During cell division the nucleoli disap- 
pear and reappear in the two nuclei of the daughter cells when 
cell division is completed. 
The protoplasm of the cell outside of the nucleus is called the 
“cytoplasm.” It will be seen to be clear and granular-looking. 
Within the cytoplasm will be observed a number of clear spaces. , 
These are pacoles and, because they are filled with cell sap (water 
