360 



A TEXTBOOK OF BOTANY [On. VII, 3 



than its surface, on which account very minute bodies present 

 so much surface in proportion to their weight that the lightest 

 breezes can waft them into the air and 

 carry them indefinitely. This is why 

 dust floats in the air, and with the dust 

 float the very minute spores of innumer- 

 able plants, of Ferns, Mosses, and many 

 kinds of Fungi, Mushrooms, Mold's, 

 Mildews, Blights, and the resting spores 

 of Yeasts and Bacteria ; and thus is ex- 

 plained the remarkable spread of those 

 ubiquitous organisms. The seeds of 

 some tropical Orchids are small enough 

 to be spread by this method, especially 



aS their SurfaCe is enlar g ed b y P reSenCe 



of small bladders. 



Dissemination is the basis of dispersal, 



in which the wind is the most effective 

 agent. Thus small plumed seeds as well as spores, which 

 can be lifted by light breezes, are carried over vast terri- 

 tories by great gales, even from island to island, and conti- 

 nent to continent. 



4. Flotage by water. The currents of rivers and oceans are 

 of course important agencies of dissemination and dispersal. 

 This result is often incidental, as when 

 twigs of Willows, or even small plants 

 washed out in time of flood, are carried 

 down stream and left to take root on some 

 emerging bank. Many fruits or seeds 

 ordinarily scattered by wind float also on 

 water, and thus are carried by rivers, 

 which transport likewise the separable 

 winter buds of many Water weeds. There 



FIG. 256. 

 Dandelion, 

 one seed ; X 2. (From 

 Le Maout and De- 

 caisne.) 



FIG. 



257. The 

 of Jericho 



are striking cases in which seeds, them- Rose 

 selves heavier than water, possess arrange- 

 ments whereby they are kept buoyed up (From Bailey.) 



