gO A Study of the Vegetation of 
xerosere to its climax community, we will next consider briefly 
a hydrophytic adsere, after which we will take up the secondary - 
succession or subsere. 
The Adsere. Alnus-Salix Associes 
Distinctly hydrophytic plant communities characterized by 
Alnus sinuata, Salix scouleriana, and Pyrus sitchensis occupy 
broad wet ravines and springy places often high up on the moun- 
tain sides. The weight of the great banks of snow which drift 
over the trees and sometimes almost bury them, pushes them into 
a semi-procumbent position leaning down the slope. The alder, 
_which is usually dominant, reaches a diameter of 2-5 inches and 
a vertical height of only 12 or 15 feet, while not infrequently it 
attains a length greater than twice its height. Likewise, the 
willow and mountain ash and also the mountain maple, Acer 
glabrum douglasii, which accompany it in this habitat, are 
bent down the slopes by the weight of the snow. Because of 
the late melting of the snow in such situations and the resulting 
springy nature of the soil, coniferous tree seedlings are excluded. 
Engelmann spruce, as already indicated, often borders such alder 
thickets and in turn gives way to the cedar. 
In this tangle of semi-prostrate trees, shrubs are nearly ex- 
cluded, although Sambucus melanocarpa and Ribes lacustre occur 
rather infrequently. A dense herbaceous undergrowth which 
almost completely conceals the ground is made up of the follow- 
ing mesophytic species: 
Aconitum columbianum Disporum oreganum 
Actea spicata arguta Mertensia membranacea 
Athyrium cyclosorum Osmorhiza divaricata 
Circaea pacifica Senecio triangularis 
Claytonia asarifolia Streptopus amplexifolius 
Clintonia uniflora Thalictrum occidentale 
Disporum majus Trillium ovatum 
The preceding plant species together with certain other meso- 
phytic shrubs and herbs and hydrophytic mosses border the moun- 
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