34 
PHARMACEUTICAL BOTANY 
about through the protoplasm of the embryo sac. Later cell walls 
are laid down and endosperm is formed. The endosperm cells soon 
become fdled with abundant starch which is later to be utilized by 
the embryo during germination. 
Microscopical examination of sections of the ovary will reveal it 
to be composed of three chambers called locules within each of which 
are to be noted several inverted ovules. Each of these ovules is 
developed upon a nourishing tissue termed “ placenta ” which con- 
nects the ovules to the inner angle of the wall of the locule. The 
ovule is composed of a central prominent megasporangium or nucellus 
which is almost completely invested by two upgrown integuments 
or coverings. The opening between the tips of the inner integument 
is called the micro pyle (little gate). This is the gateway for the 
entrance of the pollen tube on its way to the nucellus. It is also 
the exit door for the hypocotyl of the embryo after the fertilized 
and ripened ovule becomes a seed. Within the nucellus, if the sec- 
tions examined have been properly fixed, will be found a megaspore 
or embryo sac. 
MATURATION OF THE POLLEN GRAIN AND FORMATION OF THE 
MALE GAMETOPHYTE 
The pollen grains (microspores) within the anther sacs all arise 
from a number of tetrads (groups of four) which are formed by the 
division and redivision of pollen mother-cells preceding them. Each 
pollen grain, after the tetrads have separated into their components, 
consists of an outer firm wall or exosporium, an inner wall or endo- 
sporium, within which will be found the region called the fovilla, 
which is nothing other than a mass of protoplasm containing a 
nucleus. Before the pollen is shed from the anther its protoplasmic 
contents undergo a series of changes leading up to the development 
of the male gametophyte. The nucleus and protoplasm enveloping 
it divide to form two cells, one a generative-cell containing a genera- 
tive nucleus, the other a tube-cell containing a tube nucleus. The 
generative nucleus then divides to form two sperm nuclei and the 
partition wall between the two cells disappears. In this condition 
the protoplasmic contents of the pollen grain constitute the male 
gametophyte. 
