HOW PLANTS ARE SCATTERED 



381 



are : aquatic grasses, rushes and sedges, polygon urns, water-dock, 

 bur-reed, arrowhead, water-plantain, pickerel-weed, alder, button- 

 bush, water-parsnip (Sium), water-hemlock (Cfcwta), water penny- 

 wort (Hydrocotyle). 



451. Distances traversed by Floating Seeds. 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 cocoanut 

 with the fibrous husk at- 

 tached, just as it fell from 

 the tree, it is easy to see 

 how well this fruit is 

 adapted for transportation 

 by water. There are al- 

 together about a hundred 

 drifting fruits known, one 

 (the Maldive nut) reach- 

 ing a Weight Of twenty tO FIG. 270. Panicle of Tickle-Grass, a 



Common Tumbleweed. 



twenty-five pounds. 



452. Burs. A large class of fruits is characterized by 

 the presence of hooks on the outer surface. These are 

 sometimes outgrowths from the ovary, sometimes from 



