The Migration of Our Forest Trees. 191 



eastern portion of ttie state, the more pronounced hills adjacent to the 

 bluffs of the Platte valley, the broad and nearly level valley of the 

 Platte river, the steep and irregular hills of the Sand Hill country, the 

 high plains, "bad lands," buttes, and mountainous ridges of the ex- 

 treme west. 



The soils of Nebraska show much of uniformity. Most of the 

 eastern portion is overlaid with loess, which becomes more sandy west- 

 ward toward the Sand Hills, while still further west it becomes more 

 clayey. These three general types of soil are more or less modified 

 locally, as by the increase of humus in the marshy borders of some 

 streams, the increase of organic matter in the drainless valleys of the 

 Sand Hills, and the alkali soils surrounding many ponds in regions 

 still further west. 



The climate of Nebraska is of the "continental" type. The rainfall 

 which reaches thirty-five inches a year in the southeastern part gradu- 

 ally decreases westward to fourteen inches. It is very unequally dis- 

 tributed throughout the year. About 30 per cent falls in the spring, 

 39 per cent in the summer, 23 per cent in the autumn, and 8 per cent 

 in the winter. The humidity of the air is generally low, and is es- 

 pecially so in the winter. The insolation is high, the days with sun- 

 shine being more than three times as many as those without. The 

 temperatures ranges are from about 100 degrees F. as the maximum 

 heat of the summer, to 30 degrees F. as the minimum of winter, the 

 former for the southern counties, and the latter for the northern. The 

 prevailing winds are from the southeast in spriijg and summer, and 

 from the northwest in the autumn and winter. The average for ten 

 years of the number of miles of wind for each season in eastern Ne- 

 braska (Lincoln) is, 28,111 in spring, 21,016 in summer, 23,586 In 

 autumn, and 23,460 in winter. 



The native trees of Nebraska have developed many devices, for 

 the distribution of their seeds, adapted to the physical factors just 

 described. These may be reduced to five general classes, viz.: Wings, 

 hairs, fleshy fruits, rolling balls, edible nuts. 



WINGS. 



Rock Pine (Pinus Scopulorum (Engelm) Lemmon). Each seed is 

 provided with a delicate membranous wing, a centimetre long and five 

 to seven millimetres wide. When the seed drops from the cone it is 

 given a whirling motion by a slight twist and bend in the plane of the 

 wing, and if caught by the wind is carried a considerable distance from 

 the parent tree. This tree occurs in the Rocky mountains from Mon- 

 tana to Wyoming and Colorado, and in Nebraska has pushed out upon 



