ENVIRONMENT 75 



The facts are that parts of Nevada, Arizona, 

 Utah, and northern Mexico were once a great 

 inland sea that the deserts now there were the 

 bed of that sea before it began its long process 

 of evaporation. 



In these regions, so far as is known, all the 

 North American cacti are supposed to have 

 originated. 



Back in the ages before the evaporation of 

 the inland sea was complete, the heat and mois- 

 ture and the chemical constituents of the sandy 

 soil combined to give many plants an opportu- 

 nity to thrive. Among these was the cactus, 

 which was an entirely different plant in appear- 

 ance from the cactus of to-day, no doubt, with 

 well-defined stalks and a multitude of thin leaves 

 like other plants. 



As the heat, which had lifted away the in- 

 land sea, began to parch the soil, the cactus 

 with the same tendency that is shown by 

 every other plant and every other living 

 thing, began to adapt itself to the changing 

 conditions. 



It gradually dropped its leaves in order to 

 prevent too rapid transpiration of the precious 

 life-supporting moisture. It sent its roots deeper 

 and deeper into the damp substratum which the 

 sun had not yet reached. It thickened its stalks 



