Botany in Colorado 23 



tions or societies, or types, except in a most general and tentative 

 sense. It is well that with the limited time at his disposal the 

 forestry student during his first summer in the mountains should 

 concentrate upon obtaining a knowledge of the woody species, 

 especially the trees. Perhaps at the same time he may note 

 something of the requirements and of the interrelations of the 

 various tree species as is suggested in a very fragmentary manner 

 in the following pages. 



It is a rather easy task to master the mere taxonomic char- 

 acters which separate the few genera and species of trees of the 

 region, but a much more difficult problem to undertake to 

 determine something of their biological or their ecological rela- 

 tions. If in addition to the specific character of the trees of the 

 forest he can derive some knowledge of herbaceous vegetation 

 such as the grasses and the sedges, the composites, mat plants, 

 chaparral, etc., his summer will prove even more enlightening, 

 because these and many others have rather clearly defined rela- 

 tions to the life history of the forest cover. So other phases of 

 forest botany such as forest fungi, the polypores, leaf-spots, the 

 rusts of conifers, and such parasitic flowering plants as mistletoe 

 so common on the conifers may well come in for a short con- 

 sideration during his busy summer. If possible, the student 

 should make a collection of such materials as here suggested to 

 take back to the University with him, for he shall have therein 

 the nucleus about which some of his future investigations may 

 shape themselves. The tendency for the ambitious student will 

 be to " load-up" with more material than he can carry out of the 

 mountains. Nevertheless my advice is to get everything pos- 

 sible, because the more he observes and collects the more will 

 he be at home in the region when he goes again. 



While the following keys deal only with the conifers it must 

 not be supposed that the arboreal vegetation of the mountains is 

 exclusively coniferous. However, the broadleaf trees are few in 

 number, and the fact remains that the forest of the Rocky 

 Mountains is essentially coniferous. The most important broad- 

 leaf tree from the biological standpoint is probably the aspen, 

 Populus tremuloides. This tree may be easily recognized by its 

 white mealy bark and its restless orbicular leaves with long 

 slender petioles. The trees occur in rather close groves on moist 

 slopes and in gulches. The aspen is the most widely distributed 

 and the most conspicuous broadleaf tree. Besides this species 

 other poplars such as Populus acuminata and Populus angusti- 

 folia with narrow leaves are common along the lower courses of 

 many mountain streams. In addition to the poplars the fol- 

 lowing small trees are quite common along streams: alder, 



