THE FLOWER 



237 



344 345 



Figs. 344, 345. — Flower of fireweed {Epilohium an- 

 gustifolium) : 344, with mature stamens and immature 

 pi3til ; 345, the same a few days older, with expanded 

 pistil after the anthers have shed their pollen. (After 

 Grav.) 



are dioecious, or " of two households." Draw a flowering twig 

 of oak, pine, or willow. Where are the fertile flowers situated ? 

 Notice how very much more numerous the staminate flowers 

 are than the fertile ones. Why is this necessary ? (275.) 



269. Dichogamy is the name applied to a condition where 

 the stamens and 

 pistils mature at 

 different times, 

 as in the evening 

 primrose, oxeye 

 daisy, and most 

 of the composite 

 family. It is a 

 very common 

 method in nature 

 for preventing 

 self-pollination, and quite as effective as the monoecious 

 arrangement, since it renders the flowers practically unisexual. 



270. Dimorphism denotes a condition in which the sta- 

 mens and pistils are of different relative lengths in different 

 flowers of the same species, the stamens being long and the 



pistils short in some, the pistils 

 long and the stamens short in 

 others. Flowers of this sort are 

 said to be dimorphous, or dimor- 

 phic, that is, of two forms ; and 

 some species are even trimor- 

 phic, having the two sets of 

 organs long, short, and medium, 

 respectively, in different indi- 

 viduals. Examples of dimorphic flowers are the pretty little 

 bluets {Houstonia ccprulea), the partridge berry, the swamp 

 loosestrife, and the English cowslip. Of trimorphic flowers 

 we have examples in the wood sorrel and the spiked loosestrife 

 (Lythrum salicaria) of the gardens. These flowers were a 

 great pu2zle to botanists until the celebrated naturalist, 



346 347 



Figs. 346-347. — Flower of pul- 

 monaria : 346, long styled ; 347, short 

 styled. 



