THE BTOLOGICAI. CONQUEST OF 'll||.; Woiuh 



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II riijhl I'll rci 



The Russian thistle {Salsolu) introduced into this country in 1!571. Today it 

 covers the entire country. What adaptations have enabled this pesi to do tliis? 



In the world of attached animals, like sea-anemones and corals, that 

 apparently are doomed to remain in one place, the free-swimming 

 larvae seize the opportunity to break away from the maternal apron- 

 strings before settling down for life, just as stationary plants by means 

 of spores, seeds, and chmbing or trailing vegetative parts are enabled 

 to shift about and occupy new territory. Seeds of orchids and certain 

 spores of fungi, mosses, and ferns, for example, are light as dust and 

 may be wafted hundreds of miles in the air before settling down to 

 germinate on some distant soil. Seeds of dandelions and other plants, 

 such as milkweed, willow, and cottonwood, have feathery paracluite- 

 like structures, which support them in the air for some time, e\-en in a 

 wind blowing only two miles an hour. Insects, ballooning spiders, and 

 birds make use of air currents, sometimes being carried long distances, 

 particularly by heavy winds. Whole plants, like the Russian lliistl(\ 

 and the "resurrection plants" of desert regions, may dry uj) and 

 break loose from their anchoring roots, and roll along the ground or 

 ride the breeze scattering their seeds, thus taking root in newly invatknl 

 regions. 



H. w. H. — 4 



