THE STAMENS, OB ANDRECIUM. 



103 



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

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



507. THE ABSENCE of the stamens altogether, whether by abortion, 

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

 in various modes, rendering the plant monoecious ( 8 ), difficious ( $ $ ), 

 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 often elegantly 

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



Pollen grains. 367, Pinus larico. 3G3, Basella rubra. 369, Ranunculus repens. 370, Scoly- 

 mus grandiflorus. 371, Passifiora incarnata. 



509. EACH GRAIN OF POLLEN is a mem- 

 branous cell or sack containing a fluid. 

 Its coat is double, the outer is more thiok 

 and firm, exhibiting one or more breaks 

 where the inner coat, which is very thin 

 and expansible, is uncovered. In 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 



Section of tne Passion-flower (Passiflora ccerulea); 

 &, bracts of the involucre ; , sepals ; p, petals ; a,a, stami 



J c - sti i> e ; ovar ^ <*, stamens ; 



