ORGANS OF RKPKODUCTION. 



251 



diplostemenoiis flowers, as with the Willow Herb (EjnlohiKm) , 

 the stamens alternating with the petals are almost always longer 

 than those opposite to them. 



When there is a definite relation existing between the long 

 and short stamens with respect to number, certain names are 

 applied to indicate such forms of regularity. Thus in the Wall- 

 flower (Jig. o44), and Cruciferous Plants generally, there are 

 six stamens to the flower, of which four are long and arranged 

 in pairs opposite to each other, and alternating with two soli- 

 tary shorter ones ; to such an arrangement we apply the term 

 tetradynamoiis. ^NTien there are but four stamens, of which 



Fig. 543. Fig. 544. Fig. 545. 



Tig. 543. One of the bundles of stamens of Lulxea panicidata-, the inner 

 stamens on the right are longer than the others and are provided with 



anthers: the shorter stamens are generally sterile. Fig. 544. Te- 



tradynamous stamens of the Wallflower (Cheiraiithus Cheiri). Fig. 



54.5. bidyuamoiis stamens of the Foxglove (.Digitalis purpurea.) 



two are long and two short, as in Labiate Plants generally (fgs. 

 469 and 471), and in the Foxglove (Jig. 545), and most other 

 Sci'ophulariaceous Plants, they are said to be didynamous. In 

 this arrangement the two long stamens correspond to the upper 

 lip of the corolla, while the two short ones are more or less lateral. 



The Pollen. — We conclude our notice of the androecium by 

 describing the nature and characters of the pollen contained 

 within the anther. 



Development and Stnicturc. — We hare already seen that the 

 pollen corresponds to the parenchyma situated between the epi- 

 dermis of the upper and lower surfaces of the lamina of the leaf. 

 It has also been stated, that the ]>ollen is formed in certain cells 

 developed originally in the centre of the parenchyma of the 

 young antlier {fig. 498, cm) ; also that these cells were enclosed 

 in a special covering of their own {fig. 498, d), and that in the 

 course of growth they pressed upon the surrounding parenchyma, 

 ci, so as to cause its more or less complete absorption, and finally 



