1 68 On the Campus 



topographic change. There is evidence of violence, sud- 

 denness, nowhere, save in the mat pais, which is local, 

 recent, and does not affect the general problem. The 

 moving currents of the air, the soft ministrations of the 

 summer shower, the melting winter snows, have carved 

 these mountains, are sculpturing them to-day. Those 

 "columnar whirlwinds that even now like dancing der- 

 vishes chase each other across the plain, are shaping 

 anew the desert ; that thin cloud that hangs yonder like a 

 banner from the mountain top is a rainstorm, changing 

 even now the general altitude of the range. 



But once again : as we look out thus from the summit 

 of our problem we are impressed with still another fact 

 more far-reaching, more splendid still. The whole living 

 covering of the world, the vegetative garment of the 

 desert and the mountain, conforms exactly to the sur- 

 face, to soil and level, no doubt with an exactness that we 

 have only begun to guess or understand. There is a 

 mathematical line that limits the distribution of every 

 plant, but that line forever shifts and varies. The topog- 

 raphy varies, except the mat pais, by changes so slight, 

 so delicate, as to be imperceptible to eyes unskilled, and 

 with the topography varies its covering of life. 



Let us say first that these topographic changes will 

 change the limits of distribution. Once the sands cover 

 the silt plains, and the grasses will vanish while yucca and 

 artemisia succeed. Widen the talus and covillea will 

 stretch farther its golden scepter. But the problem runs 

 far deeper than this. As the face of the world undergoes 

 these delicate, subtle changes, the plant responds in 

 something far more than shifting distribution. A plant, 



