46 The Mediu7n 



slight movement of air. ZoBell calculated that if bacteria were re- 

 leased at a height of 33 m when the wind velocity was as low as 16 

 km per hr (10 miles per hr), the microbes would be carried 4800 km 

 before they reached the ground. The heights to which small or- 

 ganisms may be carried by turbulence is illustrated by a record of 

 fungal spores collected on plates exposed from an airplane at an 

 altitude of 3600 m. The rapid transport by air of spores causing 

 diseases in both plants and animals represents an ever-present threat 

 to economically important populations. New strains of, wheat rust, 

 for example, seem to be brought in by the wind almost as fast as 

 resistant types of wheat are developed. 



Many of the earth's most abundant types of higher plants, such as 

 the conifers, depend largely upon wind pollination. Pollen grains are 

 regularly transported hundreds of miles by the wind, and pollen has 

 been detected in the air over the ocean more than 1000 miles from 

 land. The seeds of orchids and of certain other groups are so small 

 that they are carried by the wind almost as effectively as pollen grains 

 and spores. Hairy structures, such as the familiar "parachutes" of 

 the dandelion, make possible the wind transport of larger seeds over 

 considerable distances, and wings, bladders, etc., such as those of the 

 maple and elm, enable many of the heavier seeds of these trees to be 

 blown far enough from the parent plants to avoid immediate com- 

 petition (Siggins, 1933). In the grasslands and desert regions yet 

 another bizarre method for transport is encountered in the tumble- 

 weed, the spherical upper portion of which breaks off and rolls for 

 miles before the wind, scattering the seeds as it goes. 



Wind also plays a significant role in the distribution of animals, par- 

 ticularly of insects. The wings of flying insects provide the lift, and 

 even ordinary winds provide horizontal translocation which may carry 

 them very great distances (Gislen, 1948). Elton (1939) found cer- 

 tain aphids and flies alive over Spitzbergen after a wind drift over the 

 ocean of about 1300 km. Stronger winds carry flightless insects, 

 spiders, and other small invertebrates in either the active or the 

 encysted condition. Strong prevailing or seasonal winds in certain 

 situations tend to exert a regular influence on the distribution of in- 

 sects. Along the northern shore of the Gulf of Mexico, human in- 

 habitants are pestered by mosquitoes regularly blown many kilom- 

 eters inland from the salt marshes by the onshore breeze, and Garrett- 

 Jones ( 1950 ) reported mass wind-borne invasions of areas as much as 



47 km from the mosquitoes' breeding places in Egypt. As compared 

 with oceanic currents, however, winds tend to be irregular, and in- 

 sects, as well as other flying land animals, can often migrate against 



