VEGETATION OF ROCKY PLACES. 609 



They hang downward, overlap on those below, and completely 

 cover the main axis or stem. The leaves of sphagnum are 

 peculiarly adapted for the purpose of taking up quantities of 

 water. Not all the cells of the leaf are green, but alternate 

 rows of cells become broadened, lose their chlorophyll, and their 

 protoplasm collapses on the inner faces of the cell-walls in such a 

 way as to form thickened lines, giving a peculiar sculpturing effect 

 to them. Perforations also take place in the walls. These empty 

 cells absorb large quantities of water, and by capillarity it is lifted 

 on from one cell to another. These pendant branches, then, which 

 envelop the sphagnum stem, lift water up from the moist sub- 

 stratum to supply the leaves and growing parts of the plant which 

 are at the upper extremity. Year by year the extension of the 

 sphagnum increases slowly upward by growth of the ends of the 

 individual plants, while the older portions below die off, partly 

 disintegrate, and pass over into the increasing solidity and bulk 

 of the peat. It thus happens sometimes that the centers of 

 such basins or moors are more elevated than the margins, be- 

 cause here a greater amount of water exists in the depths which 

 is pumped up for use in fyy the plants themselves. This is why 

 such a formation is called a "high" moor. 



Among the plants found in moors are the leather-leaf (Cas- 

 sandra), Andromeda polifolia, the cranberry, Labrador tea, etc. 

 These plants have rather small, thick, and firm leaves with a 

 thick cuticle and the under surface in some species provided 

 with scales or hairs to lessen the amount of transpiration. An- 

 dromeda polifolia has narrow leaves with a thick cuticle and 

 the edges are inrolled. The Labrador tea has small elliptical 

 leaves with a thick cuticle and the under surface covered with 

 a dense mat of hairs. The moors are often found where were 

 formerly small shallow ponds, or are found on the shores of 

 larger bodies of water. The rapid accumulation of vegetable 

 matter where it only partially decays, builds up the ground floor 

 to such an extent as to completely fill smaller ponds or lakes 

 which are not very deep. In the high moor this ground is built 

 up more rapidly than in the meadow-moor, and eventually, when 



