THE FLOWER 237 
” 
are diecious, 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 
345 
family. It is &  — sygs, 344, 345.—Flower of fireweed (Epilobium an- 
very common  sustifolium) : 344, with mature stamens and immature 
‘ pistil ; 345, the same a few days older, with expanded 
method in nature pistil after the anthers have shed their pollen. (After 
for preventing G4) 
self-pollination, and quite as effective as the moncecious 
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- 
he ae pul. ? hie). naveng vet yas Bets ef 
monaria : 346, long styled ; 347,short Organs long, short, and medium, 
styled. respectively, in different indi- 
viduals. Examples of dimorphic flowers are the pretty little 
bluets (Houstonia cerulea), 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 puzzle to botanists until the celebrated naturalist, 
