474 PHARMACEUTICAL BOTANY 
sporangium 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 micropyle (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 sections examined have been properly 
fixed, will be found a megaspore or embryo sac. 
The megasporangium or nucellus is formed from a mass of 
meristem on the placenta. While in the state of differentiation, 
one of its cells is set apart as a megaspore mother cell. Its nucleus 
(containing 2x chromosomes) undergoes two successive divisions 
during the first of. which a reduction in the number of chromo- 
- somes from the diploid (2x) to the haploid (x) number occurs. The 
x number persists in the ovum or egg. 
DEVELOPMENT OF THE FEMALE GAMETOPHYTE THROUGH THE 
MATURATION OF THE EmBryo Sac.—In its immature condition 
the embryo sac (megaspore) contains a mass of protoplasm surround- 
ing a nucleus. ‘This nucleus undergoes three divisions forming, 
as a result, eight nuclei which ultimately arrange themselves 
within the protoplasm of the embryo sac as follows: three of them 
occupy a position at the apex, the lower nucleus of the group 
being that of the egg or ovum, the other two nuclei being the 
synergids or assisting nuclei; at the opposite end of the sac three 
nuclei known as antipodals take their position; the two remaining 
nuclei called polar nuclei take up a position near the center of the 
embryo sac. In this condition the contents of the embryo sac 
constitutes the female gametophyte. [See Fig. 358 (1-8).] 
MATURATION OF THE POLLEN GRAIN AND FORMATION OF THE 
Mae 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. 
The pollen mother cells like the rest of the sporophyte generation 
contain the diploid or 2x number of chromosomes. During 
their division to form tetrads a reduction division occurs which 
reduces the chromosomes to the haploid or x number. This 
