132 DISSEMINATION OF SEEDS. 



much force as if they were spent shot from a gun. I 

 gathered a number of capsules to learn the cause of the 

 projecting force and the measure of its power. Laying 

 the capsules on the floor, I found the seeds thrown gener- 

 ally from four to six feet and, in one case, twelve feet 

 away. The cause was the contracting of the horny endo- 

 carp surrounding the seed. The seeds were oval and in a 

 smooth, bony envelope and when this had burst and ex- 

 panded enough to get just beyond the middle where the 

 seed narrowed again, the contraction of the endocarp 

 caused the seed to slip out with force." 



The woody fruit of the sand-box-tree, an American 

 tree of the order EuphorbiaceBe, Hura crepitans, is com- 

 posed of from twelve to eighteen cocci which, having 

 become dry, open suddenly at the back with two valves 

 and are detached from their axis with a kind of detona- 

 tion. "These fruits have been actually surrounded by 

 iron wires, yet the force with which they expand has 

 been such that the valves have been separated from one 

 another." 



DISSEMINATION ASSISTED BY THE ACTION OF MOISTURE 

 UPON THE FRUIT. 



"The fruit of Erodium gruinum," says Sachs, "and of 

 other Geraniaceae splits up into five mericarps each of 

 which has the form of a cone with the apex pointing 

 downwards, containing the seed and bearing a long awn. 

 When moist this awn is stretched out straight, but if it 

 becomes dry while lying on the ground, the outer side 

 of the awn contracts strongly, causing the upper end to 

 describe a sickle-like curve which brings its point against 

 the ground, the cone being thus placed with its apex 

 downwards. The lower part of the awn now begins to 



