THE WORK OF WINDS AND INSECTS 151 



After quite another fashion behave the stamen-flowers. 

 They also take shape out of sight far below, encased in a 

 bladder through which no damp may penetrate. But 

 instead of only one flower, the sac contains many; 

 and when they gain a certain stage, the enclosing sac 

 opens to set them free. Then, in place of growing 

 upward on a long stalk, they break short off and spring 



m'^^r 



VALLISNEBIA SPIRALIS. 



to the surface, at the time when their pollen is just 

 ripe. 



On first arrival at the surface they are fast shut, 

 and rounded like little globes; but soon they open, to 

 float as tiny boats on pond or lake. Wonderful little 

 boats, too — ^three flowers joined together forming one 

 boat — supported by three outspread sepals, and so 

 constructed as not to overturn even when blown 

 about somewhat roughly. They have power to right 



