670 TRANSACTIONS OF SECTION K. 
shore currents, and running water are ever destroying here and constructing 
there. Wind and water erosion cause retrogression from the ultimate 
toward more proximate stages. However, after retrogression has reached a 
certain point, continued erosion results in no further change, thus furnish- 
ing an interesting instance of change unaccompanied by succession. If 
erosion ceases, the ordinary successions of stable topography follow. Where 
winds and waters deposit, there may or may not be succession; for 
example, the slow deposition of a river commonly favours a rapid advance 
toward ‘the ultimate formation of the region, while deposition in a dune 
region may be sufficiently rapid to result in a continuation of the same 
plant conditions; if deposition slows down or ceases, the ordinary succes- 
sions of stable topography follow. 
Changes in the general climate of a region must influence succession, 
but such changes are much slower than are those previously mentioned. 
It is mainly from the geological record that we know of phenomena of 
this kind. As past climates have become colder or warmer, or drier or 
moister, respective successions toward more boreal or austral, or more 
xerophytic or mesophytic formations have taken place. 
It seems clear, then, that only when we are dealing with the ultimate 
formation of a region (the climatic formation of Schimper) is succession 
unlikely to be found. It also seems clear that succession has many causes, 
and more than those mentioned are to be expected. Furthermore, in any 
given succession it is to be expected that two or more causes co-operate, 
and it is probable that further study will increase the complexity rather 
than diminish it. Yet another bit is added to this complexity through 
the fact, just beginning to be realised, that change in external conditions 
may in many cases result in imperfect succession or no succession at all. 
A shallow pond that is dominated by an association composed of 
Proserpinaca, Radicula, Polygonum, and Sium may gradually become a 
marsh, quite a new condition, and yet be dominated by the same species 
as before; the plants change their aspect, but remain. Similarly, a spruce 
bog may gradually develop into a spruce forest, the trees changing in form 
but not in kind. Even here, however, some species change, and these may 
be taken as indices of an essential succession, even though the more con- 
spicuous species stay on. Obviously, the determination of the causes of 
succession and their exact study have but just begun. No more promising 
lead for the future seems offered, and none to which more may be contributed 
by exact observation and experiment. 
3. The Rocky Mountain Flora as Related 10 Climate. 
By Professor Francis RAMALEY. 
In general an increase of altitude in any one district lowers temperature 
about three degrees Fahrenheit for each 1,000 feet. The so-called effects of 
‘altitude’ upon plant life are, for the most part, merely the results of 
diminished heat. 
The flora of the Rocky Mountains is much the same from Canada to 
Colorado, but any particular species must be looked for at higher and 
higher altitudes as the observer travels to the south. Thus the common 
‘loco weed’ (Aragallus lamberti) flourishes at 4,000 to 5,000 feet on the 
prairies of Alberta and in the foothills near Banff, but does not reach to 
high altitudes. In Colorado it grows at these lower levels, and is also 
abundant in the mountain parks at 8,000 or even 9,000 feet. 
The mean temperatures for the summer months at Banff (altitude, 
4,542 feet) are 46, 52, and 51 degrees Fahrenheit. These are nearly the 
same as those at stations in Colorado at 9,500 to 10,000 feet. The difference 
in latitude is about 12 degrees. Roughly speaking, in this case one degree 
