4'J STKUCTUKAL BOTANY. 



in Orchis. Inequality in length is definitely marked in two 

 cases, as tetradynamous (<fs~pacr, four, 50va/jw.c, power) when the sta- 

 mens are six, whereof four are longer than the other two, as in 

 all the Crucifers ; didynamous, where the stamens are four, two 

 of them longer than the other two, as in all the Labiates (104, 106). 

 120. Cohesion is as frequent with stamens as with petals. 

 They are monadelphous (cl#eX<poV, a brother) when they are all 

 united, as in Mallow, into one set or brotherhood by the fila- 

 ments ; diadelphous in two sets, whether equal or unequal, as in 

 Pea, Squirrel-corn; polyadelph&u*^ many sets, as in St. Johns- 

 wort ; and syngenesious, when they are united by their anthers, 

 as in the Composite. Finally, the absence of the stamens alto- 

 gether, whether by abortion, as in the $ flowers of Veratrum, 

 or by suppression, as in Oak, occurs in various modes, render- 

 ing the plant monoecious (#), dioecious (6 $), or polygamous 

 ($ % ?), as already explained ( 67). 



no 



Polle.n ijrainx. 107, i'inus larico. 108, Basella rubra. 109, Ranunculus repens. 110, Scoiymus grand!- 

 horns. Ill, Passittora incarnata. 



121. The pollen is in appearance a small, yellow dust, con- 

 tained in the cells of the anther. When viewed with the mi- 

 croscope it appears as grains of various forms, usually spheroidal 

 or oval, sometimes triangular 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. Each grain of pollen is a membranous 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 



