1901 | GENETIC DEVELOPMENT OF FORESTS 3°97 
the longer the rocks have been subject to sub-aerial influences 
the more nearly they approach the condition of the climax 
plant society. 
On the sand formations at the contact of the lake with the 
shore the hydrodynamic factors absolutely prevent plant growth. 


This forest alse 
—Norway pine forest on an old beach near Marquette. 
pontithe. a top white and jack pin 
Here likewise, where the rocks dip beneath the lake, there is a 
zone of no vegetation. However, often within the reach of not 
too active waves lichens are found. Many lichens need no soil ; 
such are essentially lithophytes and are soil makers. They are 
fastened firmly to the rocks by. holdfasts which. secrete acids 
that aid in disintegrating the rocks on.which the lichens grow. 
Lichens receive moisture from the rain that falls on them, or, 
when near the water’s edge, from the wash of the waves. 
Between rains they dry and curl up, but are uninjured, for after 
