WHITE PINE 101 



female gametophyte which consists of an embryo sac con- 

 taining several greatly reduced archegonia. Each arche- 

 gonium consists of a neck made up of only four cells, a venter 

 composed of one layer of cells and containing the egg cell, and 

 a ventral canal cell, which disintegrates when the egg is mature. 



(6) Staminate Cones occur in the axils of the scale leaves 

 growing on the youngest stems. Each cone is a modified 

 branch and it consists of a central axis bearing numerous 

 spirally arranged scale-like microsporophylls or stamens. 

 The stamens (microsporophylls) bear two sporangia (spore 

 cases) containing the spore mother cells, each of which divides 

 into four cells. Each of the four cells develops into a micro- 

 spore or pollen grain which is an asexual spore. A microspore 

 is yellowish and it consists of a central reproductive body 

 and two air-sacs. 



Distribution of Pollen. When the pollen grains are mature 

 the stamens elongate and separate. The sporangial wall 

 opens, the pollen grains fall out and are carried about by the 

 air currents. 



Pollination. Pollen grains carried by the air currents fall 

 through the micropyle and into the pollen chamber which 

 is filled with a sticky fluid. 



Development of the Male Gametophyte. The central repro- 

 ductive body develops into the male gametophyte which 

 consists of two prothallial cells, which later disappear, a 

 generative cell and a tube cell. The gametophyte is, therefore, 

 greatly reduced and develops within the pollen grain, the 

 whole structure being microscopic. 



Development of the Sperms. In the fluid of the pollen 

 chamber the tube cell of the pollen grain develops a pollen 

 tube which secures food for its further growth by dissolving 

 the cells of the nucellus or the tissues external to the arche- 

 gonia. During the elongation of the pollen tube, the tube 



