The White Moss Loch. 
H5 
prevailing west to north-west wind by the tall reeds, and is covered 
so closely by the floating leaves of Potamogeton natans that few 
other species either floating or submerged occur. To the south 
and east sides the water is exposed to the wind, and on these sides 
broad-leaved floating plants are rare, their place being taken on 
the south side by Myriophyllum spicatum. This plant is adapted 
to wave motion, and its narrow leaves permit of considerable 
illumination of the bottom so that here a fairly dense lower storey 
of vegetation occurs. The accumulation of sand to about a foot in 
depth along the eastern side is due to wave action, and it is on this 
sandy bottom that Chara aspera var. subinermis forms a dense 
growth. Landwards, amongst the reeds on a similar substratum, 
Litorella lacustris is abundant. In such protected shallows 
Crampton found these species in the lochs of Caithness. 1 
In considering the reed-swamp it is difficult to say what has 
determined its distribution into the two communities already 
described. It is probably accidental that Phragmites does not 
occur on the south side, although the exposure of this side to wave 
action may have something to do with the absence of the plant. 
Phragmites is commonly absent from wave-beaten shores. It is 
only a few years ago, however, since the reed was confined entirely 
to the north side, but now the plants are extending round the 
eastern shore which is quite as much exposed as the south. In a 
short time they will undoubtedly meet the advancing extremity of 
the Carex consocies, for the distance which remains to be covered 
is small (see Map, Fig. 1). Already the zones have met at the west 
side and the dividing line between their extremities is remarkably 
distinct. Whether a struggle will occur between the reed and 
sedge, and whether the reed will ultimately establish itself right 
round the loch are interesting questions which time may determine. 
Meanwhile, both consocies are advancing inwards, and the struggle 
predicted may occur along a line from east to west now occupied 
by the open water. 
In the herbaceous marsh a difference in the water-level 
separates the Carex-Menyanthes community from the Comarum 
palustre one, and alters their floristic composition. 2 “ A change in 
the water-level very materially aids the plant dynamics in bringing 
about succession.” 3 In the Carex-Menyanthes community, water 
1 C. B. Crampton. “The Vegetation of Caithness,” 1911, p. 73. 
2 R. H. Yapp, l.c., p. 72; E. Warming, “ Ecology of Plants,” 1909, p. 348. 
* F. C. Gates, l.c. 
