272 



Rydberg disagree greatly as to the limitations of the 

 species of CastiUeja, and it is probable that much remains 

 to be done before the Colorado species are properly under- 

 stood. It can hardly be doubted that hybrids are more 

 or less frequent. 



21. Rydhergia grandiflora (T. & G.) Greene. This species, with 



its large orange heads, was very conspicuous everywhere 

 above timber line. It is one of the very few plants of 

 austral origin which have pushed their way up into the 

 high alpine zone, being in fact a sort of glorified Hy- 

 menoxys or Tetraneuris. It is singular that the one 

 member of this alliance which has reached these seemingly 

 inhospitable heights should have by far the finest and 

 largest flower-heads of all. 



22. Artemisia scopulorum Gray. Common above timber line; 



a genuinely alpine species, apparently not found in the 

 zone below. 



23. Senecio rosulatus Rydberg. Abundant on dry hills at Estes 



Park Village. At one place we found several plants of a 

 form (mut. primulinus, nov.) with pale primrose-yellow 

 rays; a variation analogous to that seen in the cultivated 

 "primrose" sunflower. 

 Palaeobotany teaches us that many of the better defined 

 genera of plants are of enormous antiquity. The careful work 

 of C. and E. M. Reid has shown that modern species at least 

 commonly date as far back as the Pleistocene, while in a number 

 of instances there appears to have been no appreciable change 

 since the Pliocene. On the other hand, the living flora is con- 

 stantly mutating, producing variations or sports, which follow 

 well established lines and can almost be predicted. It is as 

 though we had before us a seething mixture, in which different 

 elements came to the surface from time to time. The red sun- 

 flower, originating, so far as we know, in a single plant found by 

 the roadside in Boulder, was a striking novelty among sun- 

 flowers. In spite of the enormous numbers of the Helianihus 

 annuus group growing wild and in cultivation, no one, so far as 

 can be determined, had ever seen such a plant before. Never- 



