Pollen 



117 



Within the anther lobes there are developed the pollen 

 grains (fig. 218). In the early stages of the growth of the 

 anthers there are a large number of cells forming the central 

 part of each lobe. These are the parent or mother cells of the 

 pollen grains. Each of these, by cell division, becomes divided 

 into four special parent cells, and in each, by a process known 

 as free cell formation, a pollen grain is formed. In free eel 

 formation the protoplasm aggregates around the nucleus of the 

 mother cell, a cellulose coat is formed around it, and thus for a 

 while we have a cell within a cell. As the pollen grains grow 

 the walls of the special mother cells and mother cells generally 

 become absorbed and disappear, and the grains thus become 

 ir. III. IV. 



loose in the cavity of the lobe. Some- 

 times, however, the wall of the special 

 parent cells is not quite absorbed, and 

 there is formed a component body of four 

 pollen cells united, whilst in the Orchids 

 the pollen cells of each lobe are completely 

 united together, forming a pollen mass or 

 poUinium (fig. 218, v.). Each pollen grain 

 possesses two coats : the inner one, the 

 intine, is complete ; the outer one, the 

 extine, is pierced by several openings, and 

 is often variously ornamented by spines, 

 protuberances, or reticulations (see fig. 

 218). The protoplasmic contents of the 

 cell, known as fovilla, contain sulphur and fat globules. In 

 form the pollen granules are generally round ; in, the Chicory 

 they are polyhedral ; in the Evening Primrose, triangular ; in 

 the Basella, cubical ; in the Tradescantia, cylindrical ; and in 

 the Zostera, thread-like. 



Fig. 2t8. — Pollen grains 

 I. Cucurbita. JI. 

 ^assijlora. III. Cu- 

 ^hedpltttycenira. IV. 

 DipsacHS /ulloniim. 

 V. Pollen-masses (pol- 

 linia) of Cynanclntni 

 I 'incetoxicunt (Ascle- 

 piadeEe). 



