44 PHARMACEUTICAL BOTANY 
the cytoplasm of many cells. ‘They take a deep stain with basic 
dyes, like chromatin, but their significance is not understood. 
PLasMopEsMA.—The protoplasts of adjacent cells in many 
plant organs especially those possessing thick cell walls are con- 
nected by delicate threads of cytoplasm which pass through tiny 
holes (pits) in the walls between the cells. These protoplasmic 
connections are called plasmodesma. They are probably more 
common between cells with non-lignified walls than is generally 
realized owing to their frequent extreme fineness and the need 
of a special method of fixing and staining of preparations to 
bring them out. They occur in meristem, medullary rays, 
storage tissue, phloem, etc. The author has found large and 
prominent plasmodesma in the endosperm of species of Plantago 
yielding Psyllium seeds. They have been found in the red 
algze, in stems of mistletoe and pine, in nearly every part of the 
mosses, ferns, and gymnosperms, especially in the young con- 
dition of the cells, and in the thick walled endosperm of seeds of 
nux vomica, ignatia, date, persimmon, etc. (See Fig. 22:) 
CELL FORMATION AND REPRODUCTION © 
The cells of plants have all been derived from preéxisting 
cells. In the bacteria and many other low forms of plant life, 
the division of the cell always results in reproduction; in higher 
forms, however, it merely increases the size of the individual 
and so is a phenomenon of growth. 
There are two kinds of cells formed by plants, viz.: asexual and 
sexual. Both of these are endowed with the possibilities of repro- 
duction, although the former are frequently limited to the process 
of growth. 
Reproduction is the power possessed by an organism of giving 
rise to new individuals. This may take place through the agency 
of either asexual or sexual cells and is accordingly asexual or 
sexual in character. Whenever a union of cells or their proto- 
plasmic contents takes place the process is called ‘‘sexual repro- 
duction’ ; if, however, there is a mere separation of a cell or cells. 
from an individual which later form a new organism, the process 
is termed “‘asexual or vegetative reproduction.” 
