Butters: plant distribution in the Selkirk mountains 325 



on the hillsides on both sides of the glacier tongue, must have 

 reached the south moraine in far greater numbers than the seeds 

 of the plants which actually occupy it — plants in many cases rare in 

 the Selkirk range. 



The difference in vegetation must therefore be sought in actual 

 dift'erences in the ability of the two moraines to support certain 

 plants, and, as pointed out in the introductory paragraphs, the 

 moraines are essentially alike in general physical soil composition, 

 in exposure to sunlight, and in water supply. In all these respects 

 there are much greater differences between different portions of the 

 same moraine than between either moraine as a whole and the other 

 moraine as a whole. We are forced to conclude, therefore, that the 

 effective factor is the different chemical composition of the soil — 

 the presence of large quantities of limestone in the right moraine, 

 and its absence from most parts of the left moraine where granitic 

 debris takes its place. It should be further noted that as a limiting 

 factor this chemical dift'erence appears to act directly on the plants, 

 and not through the medium of plant competition. In the newer 

 parts of the moraines the formation is still open, and there is little 

 or no competition. The plants that have become established are 

 usualty far apart and there are abundant opportunities between them 

 for any other plant to become established which can grow in the soil 

 and under the somewhat rigorous climatic conditions of the region. 

 Yet a glance at the supplementary table, I : A, 2, will show that 

 exactly the same conditions obtain in these new portions as else- 

 where. 



The general distribution of the characteristic plants of the 

 south moraine is very interesting. The most abundant rocks of the 

 Selkirk range are quartzites and quartz-schists. Limestones are 

 very rare and local in their occurrence. In the main range of .the 

 Canadian Rocky mountains, however, limestones are very abundant, 

 and are present in almost all moraines and talus slopes. Nearly every 

 plant recorded in tables I : A and I : B is abundant in similar situa- 

 tions throughout the Canadian Rocky mountains, while of those not 

 occurring also on the north moraine, many are known to occur 

 elsewhere in the Selkirk range only in a very few places, and then 

 only on known outcrops of limestone, or on debris which, from its 

 situation in relation to such outcrops, presumably contains fragments 

 of limestone. These statements are based largely on personal 

 observations made during nine summers spent largely in these two 



