CBOSS-FHRTILIZATION, CONCLUDED 245 



of pollen. That is, there is most rigid econoray 

 in their make-up. It is an expensive business to 

 advertise for insects: there must be a high de- 

 velopment of color or odor (sometimes of both) , 

 large quantities of pollen, long peduncles, and the 

 like. It is also wasteful of pollen to trust to the 

 wind, as one may prove by shaking the staminate 

 cones of pines or the catkins of the birches or 

 walnuts and observing the showers of pollen which 

 are discharged. All these expenditures tax the 

 energy of the plant. The cleistogamous flowers 

 are very fruitful. It is now generally held that 

 they have been developed as a matter of economy, 

 while the seeds of the showy cross-fertilized flow- 

 ers impart sufficient vigor to the race, from time 

 to time, to prevent it from running out. This 

 explanation seems to account for the facts, and it 

 is probably correct; but a hypothesis which merely 

 accounts for the facts is not necessarily true. 

 There may be other reasons why cleistogamous 

 flowers have been developed. At all events, we 

 must be careful not to explain everything upon the 

 theory of adaptation. 



Suggestions. — There is soareely a flower which will not yield 

 some unexpected interest if one watches it when insects are work- 

 ing upon it. Flowers of very irregular and striking shape, and with 

 oddly constructed stamens and pistils, are usually specialized appar- 

 ently for insuring cross-pollination by insects. Some aquatic plants 

 east their pollen upon the water, and it is thus carried to the pistils 

 of other flowers. Birds and snails sometimes aid in transferring pollen. 



