ECOLOGY 149 



The absence of cold weather in tropical countries allows trees to mature 

 without a thick coating of bark or corky material. The trees all have a 

 green and fresh appearance. Monocotyledonous plants prevail. Ferns of 

 all varieties, especially the largest tree ferns, are abundant. 



Plant Life in the Temperate Zones. — In the state of New York con- 

 ditions are those of a typical temperate flora. Extremes of cold and heat are 

 found, the temperature ranging from 30° Fahrenheit below zero in the win- 

 ter to 100° or over in the summer. Conditions of moisture show an average 

 rainfall of from 60 to 130 cm. Cond'tions of moisture in the country cause 

 great differences in the plant covering. 



In the eastern part of the United States the rainfall is sufficient to give 

 foothold to great forests, which aid in keeping the water in the soil. In the 

 middle West the rainfall is less, the prairies are covered with grasses and other 

 plants which have become adapted to withstand dryness. In the desert 

 region of the Southwest we find true xerophytes, cacti, switch plants, 

 yuccas, and others, all plants which are adapted to withstand almost total 

 absence of moisture. In the temperate zone the water supply is the pri- 

 mary factor which determines the form of plant growth. 



Reference Books 

 for the pupil 



Andrews, Botany All the Year Round. American Book Company. 

 Leavitt, Outlines of Botany. American Book Company. 

 Coulter, Plant Relations. D. Appleton and Company. 

 Stevens, Introduction to Botany. D. C. Heath and Company. 



FOR the teacher 



Bailey, The Survival of the Unlike. The Macmillan Company. 



Darwin, Animals and Plants under Domestication, Chaps. IX, XII. D. Appleton 



and Company. 

 Kerner. Natural History of Plants. 4 Vols. Henry Holt and Company. 

 Schimper, Plant Geography. Clarendon Press. 

 Year Book, Department of Agriculture, 1894, 1895, 1898, 1900. 



