460 RYDBERG: PHYTOGEOGRAPHICAL NOTES 
Alpine lake formation 
Alpine mat formation 
Alpine rock-field formation 
While my observations at other places in the Rockies agree 
essentially in most respects with Professor Clements’ arrangement, 
it cannot be applied without modification to all localities in the 
Rockies, not even to all in Colorado. When the whole of the 
southern Rockies is considered, some modifications must be made, 
and if the alpine region of the northern Rockies is included, still 
more adjustment is needed. Here there are found formations of 
ericaceous plants, consisting of undershrubs, if not, as in the Alps, 
of shrubs. Perhaps I lay too much stress upon the moisture in 
the ground and soil, and therefore would be inclined to subdivide 
Professor Clements’ alpine meadow formation. 
The Rocky Mountains have received their name from the 
numerous loose rocks that cover their tops and sides. In naming 
plants from the Rocky Mountains, the specific name usually 
used has been scopulorum. This is really a misnomer, for it is 
not from scopulum (a projecting cliff) but from saxum (the loose 
rock), that the Rockies were named. When the mountain dis- 
integrates it breaks up into large blocks. These in the Rockies 
cover large fields, or, as they are mostly on the slopes, they are 
often more or less in motion and are usually known as “rock- 
slides.” The first form of vegetation which appears on a newly 
formed rock-slide is, of course, lichens. Whenever there has been 
deposited a little humus between the rocks a few flowering plants 
appear, mostly perennials, with strong root systems or with strong 
thizomes. Thus arises the first formation, the 
ROCK-SLIDE FORMATION 
If the rocks disintegrate still more, they become broken up into 
smaller pieces and more humus is added and there arises a gravel- 
field. If the disintegrated portion is rather thin, as it usually is 
on the top of the peaks and along the ridges, the formation is a 
xerophytic one, as little of the water from the melting snow is 
retained. So we have our second formation, which corresponds 
to Dr. Clements’ alpine mat formation. This may be called the 
