442 



HOW PLANTS ARE SCATTERED 



Ocean currents furnish transportation for the longest journeys 

 that are made by floating seeds. It is a well-known fact that 

 cocoa palms are among the first plants to spring up on newly 

 formed coral islands. The nuts from which these palms grew 

 may readily have floated a thousand miles or more without 



injury. On examining a cocoa- 

 nut with the fibrous husk at- 

 tached, just as it falls from the 

 tree, it is easy to see how well 

 this fruit is adapted for trans- 

 portation by water. There are 

 altogether about a hundred 

 drifting fruits known, one (the 

 Maldive nut) reaching a weight 

 of twenty to twenty-five 

 pounds. 



419. Burs. A large class of 

 fruits is characterized by the 

 presence of hooks on the outer 

 surface. These are sometimes 

 outgrowths from the ovary, or 

 the style (as in avens), some- 

 times from the calyx, some- 



V ' 



times from an involucre. Their 

 office is to attach the fruit to 

 the hair or fur of passing ani- 

 mals. Often, as in sticktights 

 (Fig. 344 A, B), the hooks are 

 comparatively weak, but in 

 other cases, as in the cocklebur (Fig. 344 D), and still more in 

 the Martynia (the fruit of which in the green condition is much 

 used for pickles), the hooks are exceedingly strong. Cockleburs 

 can hardly be removed from the tails of horses and cattle, into 

 which they have become matted, without cutting out all the 

 hairs to which they are fastened. 



FIG. 342. Panicle of tickle grass, a 

 common tumbleweed 



After Host 



