148 



UNIVERSITY OF COLORADO STUDIES 



little precipitation but for the fact that by far the greater part of the 

 year's rain falls during the spring and early summer. Were it distrib- 

 uted more evenly throughout the year, there would not be enough during 

 the growing season to support even this small amount of vegetation. 

 This unequal distribution of rainfall is characteristic of arid climates. 

 In more humid climates there is a more general distribution throughout 

 the year. A comparison of these two conditions is shown in the accom- 

 panying diagrams. Cheyenne with a rainfall of 12.20 inches is taken 

 as a type of the arid region and St. Louis with 40 inches is used as a 

 type of the more humid. The rainfall for the different months is shown 

 in inches. The temperature of this region presents no local features of 



r5- 





^- Q ^ 





Monthly Distribution of Rainfall at St. Louis, Mo., and Cheyenne, Wyo. 

 (See Explanation in Text) 



interest. The winters are cold, the summers hot. The extremes 

 between day and night are considerable, as is common in arid climates. 

 The work of this expedition is but the beginning of what the Univer- 

 sity hopes in time to be able to do. Here in Colorado the naturalist has 

 before him a very exceptional field. In a large part of the state little 

 scientific work has been done. The wide diversity of climatic condi- 

 tions occurring within the state, from mountain to plain, support a 

 flora and fauna of corresponding variety. There are already known in 

 Colorado over 2,900 species of seed-plants and ferns, a number exceeded 

 by no other state in the union but California and possibly Florida.' 

 We have here a field for research and exploration in which very little 

 has been done. In working this field we need have no fear of duplicating 



■ Rydberg, Flora of Colorado, p. xv, 1906. 



