RELATION OF PLANTS TO ENVIRONMENT 459 



" Bad Lands " cf Dakota and Nebraska, and in alkaline soils of 

 the Southwest and California. These plants are able to with- 

 stand a stronger concentration of salts in the water or soil mois- 

 ture than other plants. They are also found in soil about salt 

 springs. 



Fig. 417. 



Bad Lands. Pinus ponderosa scopularum on the talus of huttes on the borders of Sow- 

 belly Canyon, Pine Ridge, Nebraska. Bouteloua oligostachya (grama grass) formation in 

 foreground (Dept. Geol., iv. Nebr.). 



625. Tropophytes.* Tropophytes are plants which can live 

 as mesophytes during the growing season, and then turn to a 

 xerophyte habit in the resting season. Deciduous trees and 

 shrubs, and perennial herbs of our temperate regions, are in this 

 sense tropophytes, while many are at the same time mesophytes 

 if they exist in the portions of the temperate region where rain- 

 fall is abundant. In the spring and summer they have broad 

 and comparatively thin leaves, transpiration goes on rapidly, but 

 there is an abundance of moisture in the soil, so that root absorp- 

 tion quickly replaces the loss and the plant does not suffer. In 



* Term used by Schimper, rpoiros, from Tpeirew = to turn, <J>VTOV= plant. 



