-31- 
ioo usually roach much higher than this, and thus mark out 
the upper limits of u zone in which only tho hardiest per¬ 
ennials are able to survive. 
b* The shoro successions. 
Since the surface of tho lake has 
boon at tho present level for a long period of time, the 
distribution of the pioneer associations at any point along 
tho shoro has reached a balance which will remain practically 
the same so long as the climatic, ecological and historical 
factors remain unchanged* In other words, it is probably 
incorrect to say that active invasion or retrogression is 
taking place at the present time, even admitting the slight 
changes in coast line, due to subsidence or erosion. 
The pioneer associations along the shore are composed 
of crevice plants, of lichens and of mosses. On account of 
the frugraontal nature of the rooks, crevice plants appear 
to be tho moot important pioneers; most of them are per¬ 
ennials. The seeds lodge in the moist cracks of joint and 
bedding planes, and germinate even where little or no soil 
is present. Gradually the seedling intercepts enough soil 
for tho establishment of a firm root system, and then is 
able to persist for many years, and spread by means of 
offshoots. Two of the commonest and hardiest species in 
tliio connection are Juncus Dudley! W iegand and Dos champ si a 
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