Native Vegetation 
37 
growth of a crop. A very important consideration, particularly as 
regards the fruits, is the character of the winters and springs. Are 
the winters open and windy? Are there series of early warm 
days which induce the swelling of buds, and which may be fol¬ 
lowed by freezing weather? Or does the spring open gradually? 
The failure of a tender crop, like peaches, on the Plains, even in 
those sections with a long growing season, and an early date for 
the last spring frost, and warm summer months, is largely due to 
the dry, windy winters, and to the inconstancy and fluctuations of 
the spring weather. Melons find conditions for their growth and 
maturity most favorable in the southern part of the Great Plains 
steppe, where the growing season is close to 150 days, and where 
the average date of the first frost in the autumn is not earlier than 
October 1. Great Plains localities with frosts coming as early as 
the middle of September, are unsafe for melon growing as the 
fruit is usually caught, under such circumstances, about two weeks 
before maturity. 
The establishment of trees under dry land conditions in grass- 
steppe territory is a difficult, although not impossible, undertak¬ 
ing. The open winters, with their high rate of evaporation, 
droughts in July and August, the frequent low temperatures, and 
great diurnal ranges, are difficult hazards for the young tree. How¬ 
ever, once established, many of the more drought-resistant trees 
do well over the Great Plains, even on dry land. 
The absence of a snow cover during most of the winter sea¬ 
son, accompanied by a cold soil, a dry atmosphere, and a clear sky, 
is a condition which makes winter-killing from drying out a men¬ 
ace to the fruit-grower, the owner of forest tree plantations, and 
to the alfalfa-grower. The tenderer cane fruits are regularly 
buried, and strawberries mulched. 
SHRUB-STEPPE 
Distribution and Vegetation .—A large part, close to 25 per 
•cent, of Colorado, is covered with a shrub type of vegetation. The 
principal species composing this shrub-land are sagebrush ( Arte¬ 
misia tridentata) , greasewood (Sar cobat us vermiculatus) , shad- 
scale or saltbush ( A triplex conferti folia) , orache or grey salt¬ 
bush {A triplex canescens), salt sage ( A triplex nuttalli), koehia 
(Kochia vest it a) , and rabbitbrush ( Chrysothamnus species). The 
most important and by far the most extensive shrub-steppe in Col¬ 
orado is sagebrush. It is the characteristic type of vegetation of 
the arid districts of western Colorado; this region represents the 
^eastern limit of the sagebrush formation which dominates the 
