326 BOTANICAL GAZETTE [may 



t 



Pktncipal species. — Silene acaulis L., Sieversia turbinata (Rydb.) Greene, 

 Dryas octopetala L., Phlox caespitosa Nutt., Campanula rotundifolia L., 

 Rydbergia grandifiora (T. & G.) Greene. 



Secondary species.— Selaginella densa Rydb., Deschampsia caespitosa 

 alpina Vasey, Trisetum subspicatum (L.) Beauv., Carex atrata L., Juncoides 

 spicatum (L.) Kuntze, Zygadenus coloradensis Rydb., Lloydia serotina 

 Reichenb., Polygonum viviparum L., Oreobroma Grayi (Britton) Rydb,, O. 

 pygmaea (Wats.) Howell, Arenaria sajanensis Willd., Draba crassifolia Graham, 

 Sibbaldia procumbens L., Dasiphora fruticosa (L.) Rydb., Trifolium dasy- 

 phyllum T. & G., Oreoxis alpina (Gray) C. & R., Primula angustifolia Torr., 

 Androsace subumbellata (A. Nels.) Small, Douglasia Johnstonii A, Nels., 

 Polemonium confertum Gray, Mertensia viridis Nels., Castilleja puberula 

 Rydb., Pedicularis Parryi Gray, Solidago scopulorum (Gray) A. Nels., Tetra- 

 neuris acaulis (Nutt.) Greene, Tonestus pygmaeus (T. & G.) Nels., Engeron 

 pinnatisectus (Gray) Nels., Artemisia scopulorum Gray. 



2. The wet meadow 



It must be borne in mind that on account of a smaller deposit of 

 snow, due to exposure to the wind and sun, the summit of the range 

 and the unglaciated slopes were first exposed, while the canons still 

 contained glaciers fed from the neve accumulated in the cirques at 

 their upper ends. Thus it w^as long after- the dry meadows above 

 had begun their development when vegetation, following the retreat 

 of the ice, first gained access to the upper portions of the canons* At 

 the present day the spruce-fir forest extends up the canons to an 

 ahitude of about 3350^. Above this is an area supporting a meso- 

 phytic meadow vegetation, w^hich, however, only partially covers the 

 ground, being confined to the vicinity of the watercourses. Still 

 higher, where the last remnants of the ice Ungered, there is no vegeta- 

 tion save a sparse growth of Hchens. In the heads of the canons, there- 

 fore, we may study primary invasion in all its stages, and the next few 

 paragraphs will be devoted to a description of it as observed in these 

 places. 



A. The glacial canon as a habitat. — Atmospheric conditions. 

 As to the atmospheric conditions in the canons I can give no exact data, 

 but it may be said with certainty that they are comparatively favor- 

 able to plant growth— much more so than in the region of the dry 

 meadows. The most noticeable difference between the two habitats, 

 in regard to atmospheric conditions, is the exposure to the full force 

 of the wind on the dry meadows, contrasted with the effective shelter 



