BOTANICAL GAZETTE [JUNE 
dense felt of humus vegetation protects the ground from erosion. 
Fallen leaves and other organic materials swept from the forest 
- floor into the edge of the pool tend to smother the vegetation 
which might grow there, and thus is produced a belt of open 
water, surrounding an island, or if the pond is larger a ring of 
‘vegetation. 
Tempe COLLEGE, 
Philadelphia. 
