364 



NATURE-STUDY 



vided with wing-like devices for dispersal, or else tlie seeds 

 are thus provided. Elm and maple fruits have wings. The 

 seeds of the catalpa have feathery wings, and the cotton- 

 wood seeds are covered with a mass of down. Seeds and 

 fruits of trees also float upon the water and may be thus 

 scattered. Through the agency of man, orchard and shade 



Fig. 155. White Elm in Flower. 



trees are planted, and on our originally treeless prairies there 

 are now on nearl}' e\'ery farm planted groves. 



Trees, like other plants, are dependent upon temperature, 

 moisture, light, and soil. Temperature is one of the chief 

 conditions determining the distribution of species. Conifers 

 as a class prefer the colder northern regions or the higher 

 altitudes on mountains. There are, however, southern and 

 lowland species. The deciduous hardwood trees also abound 

 chiefly in the colder temper? te regions. Some, like the wil- 



