36 



H. B. HUMPHREY AND J. E. WEAVER 



on the south slope occupies dense thickets near the protected 

 base. That the south slope supports a very open forest (mostly 

 yellow pine and Douglas fir above the ravine) is shown by the 

 fact that the average number of trees per square meter is only 

 one, as compared with 3.5 per unit area on the north slope. 



No less characteristic of the two exposures are the shrubs of 

 the undergrowth. Opulaster pauciflorus, Ceanothus velutinus and 



Fig. 3. A young forest of white fir, tamarack, and cedar occupying a cut- 

 over north slope in Thatuna Hills. 



Salix scouleriana make up the chief shrubby growth on the south 

 slope, often covering many square meters exclusively. On the 

 north slope both Opulaster pauciflorus and Ceanothus velutinus 

 occur but rarely, while Vaccinium memhranaceum is more abun- 

 dant than Salix scouleriana. Coptis occidentalism Clinlonia uni- 

 flora, Thalictrum occidentale, Milella stauropetala, Galium sp., 

 Asarum caudatum, Anemone piperi, Pyrola bracteata, Cytherea 



