PLANTS ON THE MOVE 193 



it planted a thousand miles away. It is enough 

 to secure fresh soil for the seedling, and also to 

 secure in a time that is short in comparison with 

 a geological age the colonization of the largest 

 piece of land in the world. Even the thistle which 

 flies its seed only forty yards would take a thou- 

 sand years to travel twenty miles. And a tree 

 that only bore fruit at the age of thirty, and 

 then parachuted its seeds like the sycamore, 

 would take half a million years to colonize from 

 Land's End to John o' Groat's. How are we 

 going to get Claytonia, the perfoliate chickweed, 

 from America to Europe in a single season ? 



It is suggested by Kerner von Marilaun that 

 some of these shooting seeds are designed to go 

 off at the right time, so as to shoot a passing 

 animal and so get transported in its fur or feathers. 

 The case of the squirting cucumber is a strong one. 

 In this fruit the skin presses on the liquid contents, 

 against the resistance of the stalk which acts as 

 a stopper. A slight jerk from a passing animal 

 upsets the equilibrium, the stopper flies out, and 

 a stream of seeds in jelly, something like the 

 contents of a gooseberry, shoots the intruder like 

 a spring gun. Anything locomotive thus hit must, 

 of course, carry a seed or two a considerable 

 distance before dropping them. 



Most plants, however, that rely on animals to 

 transport their seeds adopt far simpler means. 

 Of all the flowering plants, one in ten have fruits 

 capable of hooking themselves at a touch to 



