THE STAMENS, OR ANDRECITTM. 



103 



phous, many sets, as in St. John'swort ; and syngencsivus, 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 Veratrum, or by suppression, as in oak, occurs 

 in various modes, rendering the plant monoecious ( 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 often elegantly 

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



871 



Pollen grains. 367, Pinus larico. 363, Basella rubra. 369, Ranunculi 

 mus grandiflorus. 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. In the fluid 

 are suspended molecules 

 of inconceivable minute- 



repens. 370, Scoly- 



tre- 

 mulous motion. When 

 the membrane is exposed 

 to moisture it swells and 

 bursts, discharging its 

 contents. 



510. POLLINIA. In 

 the Orchids and Silkweed 



3T2, Section of the Passion-flower (Passiflora ewrnleft) ; 

 Z>, bracts of the involucre ; , sepals ; p, petals ; a,a, staml 

 nodia or sterile filaments j c, stipe ; o, ovary ; 



