200 PHARMACEUTICAL BOTANY 



Plants pollinated through the agency of water currents are known as 

 Hydrophilous. To this class belong such plants as live under water 

 and which produce flowers at or near the surface of the same. Exam- 

 ple: Sparganium. 



Animal-pollinated plants are called Zoophilous. Some plants like 

 the Nasturtium and Honeysuckle are pollinated by humming birds. 



Before the pollen grain has been deposited upon the stigma and 

 during its germination thereon, a series of events affecting both the 

 pollen grain and the embryo sac occur which result in the ultimate 

 formation of the male and female gametophytes. 



Maturation of the Pollen Grain and Formation of the Male 

 Gametophyte. The substance of the microspore (pollen grain) 

 divides into two cells, the mother and tube cells of the future male 

 gametophyte. The nucleus of the mother-cell divides to form two 

 sperm nuclei. Within the tube cell is found a tube nucleus em- 

 bedded in protoplasm. Upon germinating the partition disappears 

 and the thin endospore, carrying within it the protoplasm in which 

 are embedded the tube nucleus and two sperm nuclei, penetrates 

 through a deficiency of the exospore. The contents of the pollen 

 grain at this stage is called the male gametophyte. 



Maturation of the Embryo Sac and Formation of the Female 

 Gametophyte. The nucleus of the megaspore or embryo sac under- 

 goes division until eight daughter -nuclei are produced which are 

 separated into the following groups: 



(a) Three of these nuclei occupy a position at the apex, the lower 

 nucleus of the group being the egg or ovum, the other two nuclei 

 being the synergids or assisting nuclei. 



(b) At the opposite end of the sac are three nuclei known as the 

 antipodals which apparently have no special function. 



(c) The two remaining nuclei (polar nuclei) form a group lying 

 near the center of the embryo sag which unite to form a single 

 endosperm nucleus from which, after fertilization, the endosperm or 

 nourishing material is derived. This stage of the embryo sac con- 

 stitutes the female gametophyte. 



Fertilization in Angiosperms. After the pollen grain reaches the 

 stigma, the viscid moisture of the stigma excites the outgrowth of the 

 male gametophyte which bursts through the coats of the pollen 



