THE ANGIOSPERMAE 



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enough in some climates to be important for seed dispersal. The normal 

 storms of autumn are quite capable of carrying plant debris, including 

 seeds, for distances of several miles. 



Fig. 1383. — EcbaUiiini elateiium. Ejection of seeds from a detached 

 fruit. See in text. (After Kenier and Oliver.) 



Among mountains, and in the desert, wind effects are magnified and 

 their importance increased. The only outstanding exception to the general 

 influence of wind is the undergrowth of tropical rain forests, into which 

 none but the most violent winds can penetrate, and the absence there of 

 plants with winged or plumed seeds is notable. Even the Grasses seem 

 unable to enter the forest from outside, and their seeds as well as others 

 are stopped by the dense marginal growth of the forest shrubs. 



Wind dispersal seems to be less effective across the sea than overland, 

 and plants with winged seeds or fruits are reputed to be absent from 

 islands which are more than 25 miles distant from the nearest land. Only 

 a few plumed seeds, and minute " dust " seeds, have reached remote 

 islands which were not originally joined to a continent. The last-named 

 category of dust seeds, i.e., very minute seeds, are those most widely dis- 

 persed by wind, and in some cases, such as that of the three Polynesian 

 Orchids which have reached Hawaii, they are known to travel for hundreds 

 of miles either over land or sea. Grains of quartz weighing up to 0003 



