68 THE AxMERlCAN BOTANIST. 



many flowers ensure that they shall be pollinated by pol- 

 len from other flowers by the simple exi3edient of ripening 

 the pistils and stamens at different times, so that when 

 their ow^n pollen is ready the pistils are not, or vice versa. 

 Insects going" between such flowers must bring pollen at 

 one time and carr^^ pollen at another, but with the aid of 

 petals, the flowers are able to double up on the insects and 

 make them fetch and carry at the same time. In the siin- 

 plest forms of such flowers, the petals are formed into a 

 tubular corolla and the pistils and stamens are of different 

 lengths, some flowers having long pistils and short sta- 

 mens and others the opposite. It will readily Idc seen that 

 flow^ers with short stamens and long pistils could never be 

 self-pollinated, for the stamens could not come in contact 

 with the pistils. Insects must be induced to act as go-be- 

 tweens. When therefore an insect, bent on securing the 

 nectar at the bottom of the corolla, visits a flower with 

 short stamens, the pollen is brushed by a certain partot its 

 proboscis which becomes powdered with it. When it later 

 visits a flower with a pistil of the same length as the sta- 

 mens, the latter is sure of pollination. If the insect next 

 visits a flower with long stamens, it receives pollen in just 

 the right place to pollinate the long pistils. Soon, there- 

 fore, its proboscis is likely to have two bands of pollen up- 

 on it and every flower thereafter visited, whether with 

 long or short pistils, is likely to receive its share. The co- 

 rolla closely surrounding the essential organs insures that 

 pollination must occur if the insect secures the nectar. In 

 some of the flowers of this kind there are three different 

 lengths of stamens and as man}^ different lengths of pistils, 

 giving a much wider range of crossing. 



Other flowers have different means of accomplishing 

 the same result. Many species in the bean and pea family 

 have pistils and stamens concealed by the keel formed of 

 the two lower petals. When an insect alights on the flow- 

 er the keel is depressed, allowing the pistils and stamens to 

 brush across its body, the one set to obtain any pollen that 

 maybe adhering to it, the other to deposit more pollen for 



