THE STAMENS, OR ANDRECIUM. 



103 



phous, many sets, as in St. John'swort ; and syngenesious, when they 

 arc united by their anthers, as in the Composite. Finally, 



507. The absence of the stamens altogether, whether by abortion, 

 as in the $ flowers of Veratrum, or by suppression, as in oak, occurs 

 in various modes, rendering the plant monoscious (8 ), dioecious ( £ °. ), 

 or polygamous ( <$ & ¥ ), as already explained (^ 421). 



508. The pollen is in appearance a small, yellow dust, contained in 

 the cells of the anther. When viewed with the microscope it appears 

 as grains of various forms, usually spheroidal, or oval, sometimes tri- 

 angular or polyhedral, but always of the same form and appearance in 

 the same species. Externally they are curiously, and ofteu elegantly 

 figured with stripes, bands, dots, checks, etc. 



367 



Pollen grains. 367, Pinus larico. 368, Basella rubra, 

 mus gramliflorus. 371, Passiflora incarnata. 



509. Each grain of pollen is a mem- 

 branous cell or sack containing a fluid. 

 Its coat is double, the outer is more thick 

 and firm, exhibiting one or more breaks 

 where the inner coat, which is very thin 

 and expansible, is uncovered. Iu the fluid 

 are suspended molecules 

 of inconceivable minute- 

 ness, said to possess a tre- 

 mulous motion. When 

 the membrane is exposed 

 to moisture it swells and 

 bursts, discharging its 

 contents. 



510. Pollinia. In 

 the Orchids and Silkweed 



369 370 



9, Ranunculus repens. 370, Scoly- 



872, Section of the. Passion-flower (Passiflora ererulea); 

 ft, bracts of the involucre; *, sepals ; p, petals; a,n, stami 

 nodi a or sterile filaments ; c, stipe; o, ovary; rf, stamens ; 

 t, stigmas. 



