• .. /-:k- tar d.^wii aii'l soiiiclimes entirely through the flon. 

 .M . ,K- below it. 'I1ii> is due to the stream and the cold and 



renditions in the canyon. Just the reverse of this effect is seen 



l'"Tc ne see tlie desert flora rnnnin^ far up the mountain 

 side in a reversed tong^ue, so that desert plants are actually 

 found far ahove the species of the next highr zone. This 



'I he chief chans:es in a flora are due to the falling of seeds 

 in places with a slightly different climate, to steady changes 

 of climate due to the recession of the equinoxes, to elevations 

 I r subsidence of vast areas of land and the resultant alterations 

 ly dramage, or the production of lakes and swamps, or great 

 mountain chains. These of necessity change the humidity and 

 rcnmerature and require that the life shall change correspond- 

 intrly. migrate, or be exterminated. The alterations in the 

 flora udl be in their nature internal and made with a view to 

 i!ie y^reservation of the species by resisting harmful clima- 

 te mtluences. or the propagation of the species by utilizing 

 thr vnnous means of distribution. To the student of Na- 

 ture these alterations are like the fossils in the rocks, means 

 .f reading the history of the world back to periods untouched 

 hy books or tradition. For example, the early spring flora 

 tells us of an alpine or frigid vegetation which once existed 

 here but which is now represented only by a remnant. An ab- 

 normal number of annuals tells us of a former desert flora. 

 1 lants with seeds or pods covered with hooks, barbs, or gum 

 tell us that they were created after the animals existed which 



iiitable hair or feathers for i 



orting thei 



!y toward the prese 



)st interesting phase of life is in the devices e 



esisung seasonal and climatic changes. They i 



