International Excursion in America. 
39 
were likely to be stable under the conditions to which they were 
exposed. The present writer, while accepting the succession given 
above as normal, with much disturbance and telescoping owing to 
various causes, was inclined to doubt whether the pine forest, a very 
distinct association, occurring specially on wind-swept gentle slopes 
or on the broad, rounded tops of minor summits, would not in such 
situations tend to maintain itself indefinitely. Professor Clements’s 
forthcoming book on the vegetation of this region will no doubt 
clear up many such questions. What seems to be wanted is a very 
clear statement, analysis and criticism of the evidence for the 
continuity of the sucession, of the conditions determining the 
initiation of each stage in the habitat presented by the preceding 
stage, and of the conditions under which disturbance and telescoping 
occur. 
Space does not permit of an extended account of the vegetation 
of the upper ranges of the mountains, of which indeed, partly owing 
to bad weather, we did not see as much as could have been wished. 
Above about 9,000 feet Douglas fir forest gives way to forest of 
Englemann spruce, which has much the same ground vegetation. 
Professor Schroter noted the following marked differences between 
the forest of Picea Engelmanni and the corresponding Swiss forest 
of Picea excelsa : absence in the former of plants germinating on 
fallen rotting trunks or on stumps; less humus and no specialised 
humus-plants; no Usnea on the trees. These negative features are 
no doubt to be attributed to the much drier air. Picea Engelmanni 
sometimes itself forms the upper forest-limit at 11,000 feet, but 
often gives way to Pinas aristata, which in that case forms the 
actual “ timber line ” and often presents fairly characteristic 
“ Kriippelholz ” forms. Above this there is no alpine scrub- 
association but we pass at once to alpine-meadow alternating with 
gravel-slides inhabited by quite a different set of species from those 
of lower levels. Cushion plants such as Paronychia pulvinata, 
Arenaria biflora and Silene acanlis, together with such forms as 
Haplopappus pygmceus, Senecio taraxacoides and Festuca brachyphylla 
are the characteristic species. The rock-cleft vegetation contains 
Polemonium speciosum, Primula Parryi, Mertensia alpina , Claytonia 
megarrhiza , etc. 
The alpine meadow consists primarily of Carex rupestris, C. 
filifolia , Festuca brachyphylla and Poa spp., with societies of Rydbergia 
grandijlora, Polygonum bistortoides, Mertensia alpina, Castelleia 
pallida-, and this is the main climax association above 11,000 feet. 
