VEGETATION OF ROCKY PLACES. 613 



mingled are various mosses and much sphagnum. The soil 

 formation underneath contains remains of carices, grasses, and 

 sphagnum. This intermediate zone is not a homogeneous one. 

 At certain places are extensive areas in which Carex- filiformis 

 predominates, while in another place another carex, or grasses, 

 predominate. 



A floating inner zone. But the innermost zone, that which 

 borders on the water, is in a large measure made up of the leather- 

 leaf shrub, cassandra, and is quite homogeneous. The dense 

 zone of this shrub gives the elevated appearance to the atoll 

 immediately around the central pond, and the cassandra is 

 nearly one meter in height, the "ground" being but little above 

 the level of the water. As one approaches this zone the ground 

 yields, and by swinging up and down, waves pass over a consider- 

 ble area. From this we know that underneath the mat of living 

 and recent vegetation there is water, or very thin mud, so that 

 a portion of this zone is "floating." 



The inner, or cassandra, zone is more unstable, that is, it is 

 all "afloat," though firmly anchored to the intermediate zone. 

 The roots of the shrubs interlace throughout the zone, firmly 

 anchoring all parts together, so that the wind cannot break it 

 up. Between the tufts of cassandra are often numerous open 

 places, so that the water or thin mud on which the zone floats 

 reaches the surface, and one must exercise care in walking to 

 prevent a disagreeable plunge. No resistance is offered to a 

 pole two to three meters long in thrusting it down these holes. 

 Grasses, carices, mosses, sphagnum, and occasionally nioor-loving 

 dicotyledons occur, anchored for the most part about the roots of 

 the cassandra. Standing at the inner margin of the cassandra 

 zone, one can see the mud, resembling a black ooze, formed of the 

 broken plant-remains, which have floated out from the bottom 

 of the older formations. In some places this lies very near the 

 surface, and then certain aquatic plants, like Bidens and others, 

 find a footing. Upon this black ooze the formation can continue 

 to encroach upon the central pond. Agitated by the wind, more 

 and more of the ooze passes outward, so that jn time there is a 



