ORGANS OF REPRODUCTION. 



259 



respect to each other presents several peculiarities, some of 

 which are important in descriptive botany. Sometimes, all 

 the stamens of the flower are nearly of the same length, while 

 at other times, they are very unequal. This inequality may 

 be altogether irregular again, following no definite rule, or take 

 place in a definite and regular manner. When the flowers are 

 polystemenous, the stamens nearest the centre may be longer 

 than those at the circumference, as in Luhea {fig. 545), or the 

 reverse may be the case, as in many of the Kosaceie. In the 

 case of diplostemenous flowers, as in Epilobium, the stamens 

 alternating with the petals are almost always longer than those 

 opposite to them. 



Fig. 547. 



Fig. 545. 



Fig. 546. 



Fig. 545. One of the bundles of stamens of Luhea paniculafa, the inner 

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



anthers : the others are shorter and generally sterile Fig. 546 Tetra- 



dynamous stamens of the Wallflower {Cheiranthus Cheiri) Fig. 547. 



Didynamous stamens of the Foxglove ^Digitalis purpurea). 



When there is a definite relation existing between the long 

 and short stamens with respect to number, cei'tain names 

 are applied to indicate such forms of regularity. Thus in 

 the Wallflower (fig. 546), 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 solitary shorter ones ; to such an arrangement we apply 

 the term tetradynamous. When there are but four stamens, of 

 which two are long, and two short, as in Labiate Plants generally 

 {figs. 471 and 473), and in the Foxglove {fig. 547) and many 

 other Scrophulariaceous Plants, they are said to be dichjnamous ; 

 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 stamens by 

 describing the nature of the pollen. 

 S2 



