25 



I 



vapor is a blanket more necessary to the vegetable life of England than 

 clothing is to man. Remove for a single suinmer-night the aqiieons 

 vapor from the air which overspreads this conntryj and every plant 

 capable of being destroyed by a freezing temperatnre wonld 'perish. 

 The warmth of oar fields and gardens woald pour itself unrequited 

 into space, and the sun would rise upon an island held fast in the iron 

 grip of frost." 



These, then, being the climatic conditions, somewhat, of the plains 

 during the growing period of the year, it does not seem strange that the 

 ensemble of the flora should be as pecnliar. The diurnal range of tem- 

 peratnre during the summer-months is at times immense. In South 

 Park I have seen the temperature as high as 90^ Fahr. at 2 p. m„ and 



on rising the next morning find a film of ice coating- the little accumu- 

 lations of water around camp. Oiw familiar forms of plant-life would 

 almost all be destroyed under sucli an alternation of heat and frost for 

 year after year. The plants, then, that we do find surviving are, as a 

 rule, more dwarfed, more villous, and with denser tissues than those of 

 more genial regions. Nature would ap[)ear to have especially guarded 

 them against excessive evaporation of their fluids on the one hand and 

 freezing on the other, and meeting both contingencies by a small supply 

 of water in their tissues, retaining that which they possess uiuler the 

 double guard of villosity and contraction. I am aware that Air. \Yat- 

 son, in his most valuable report on the Botany of the Fortieth Parallel, 

 is prepared to admit a large evaporation from the more succulent por- 

 tions of the plant. 



The monotonous character of the flora of the dri^r regions does, iu 

 some measure, disappear, when, on examination of these plants, so 

 uniform in general api)earauce, we find a large number of genera and 

 species differing from one another by the small amounts compatible tcith 

 their surroundings. This (the surroundings) in part accounts for the 

 predomination of some orders and often of genera. We find a some- 

 what similar condition of things in the center of greatest development 

 of the Proteacece in Australia or the Pelargoniums in South Africa. 



Comparatively few of our eastern plants are found in these open 

 grounds, and where one does occur it is apt to be a cosmopolitan wced^ 

 whose pliant constitution adapts it to any condition of life as well as 

 to the hostility of man. Polygonum aviculare and Chenopodium hybridiim 

 are examples. Among the exceptions to this statement is Baminciilus 

 cymbalaria; bat its natural habitat on the western open lands is, by 

 choice, alkaline soils, where, for a portion of the year, at least, it can 

 obtain moisture, just as with us it frequents salt-marshes and the sea- 

 shore. 



Among the mountains, on the contrary, we find a larger number of 

 familiar plants. Indeed, the list is so large that it would be a real labor 

 to begin the enumeration. Those plants embraced under the common 

 nanu* of weeds are from necessity found usually on the roadsides and 

 about habitations, just where they can be transported by human agency, 

 and find, among other essentials, water. It is wonderful with what 

 rapidity they have occupied the ground in many places. 



FLORA OF THE MOUNTAINS. 



Leaving the level ground, we at once come fairly within the range of 

 the timber. In South Park, this is not far from 10,000 feet; tongue- 

 like projections of trees do extend lower down; but 1 refer to the main 

 body of the forests. 



