48 



FLOWERS AND THEIR WORK 



surface of the water. The staminate flowers, when ripe, break away from 

 their submerged stems and float to the surface. If these float under a 

 pistillate flower, the protruding ends of the pistils catch and retain some 

 of the pollen from the staminate flower. Thus fertilization follows. 

 After pollination, the stalk of the pistillate flower coils up in a spiral and 

 draws the flower under the surface of the water, so that the seeds may 

 ripen in security. 



Summary. If we now collect our observations upon flowers 

 with a view to making a summary of the different devices flowers 



Flowers of the Lady Washington geranium showing the conditions of dichogamy ; 

 A, flower with stamens ripe, but with the stigma not ready to receive pollen ; B, 

 the same flower at a later stage ; the stamens have withered, but the stigma is now 

 ready to receive pollen. 



have assumed to prevent self-pollination and to secure cross-pollina- 

 tion, we find that they are as follows : 



(1) The stamens and pistils may be found in separate flowers, 

 either on the same or on different plants. 



(2) The stamens may produce pollen before the pistil is ready to 

 receive it, or vice versa. This condition is called dichogamy. 



(3) The stamens and pistils may be so placed with reference to each 

 other that pollination can be brought about only by outside assistance. 



In some flowers, as is shown by the primula of our hothouses, 

 the stamens and pistils are each of two different lengths in different 



