Methods of Surveying Vegetation. 235 
■of the association boundaries, the contours drawn from the spot- 
level data alone frequently follow the boundaries very closely. 
A comparison of Figs. 78 and 80 exhibits very well the greater 
detail which can be shewn on a grid as compared with a square. The 
enclosed area corresponding with Fig. 80. in the upper left hand 
corner of Fig. 78 shews, running across its lower part, a continuous 
line representing the cliff of a channel, the surface of which is 
mainly occupied by SI. ( Salicornia lierbacea). The centre of the 
Fig. 80. A mapped Gridiron with levels and contour lines. 
Two sets of “ bars ” at right angles to one another are represented. 
grid bears a uniform carpet of SI. G. ( Salicornia lierbacea, bright 
crimson in colour, mixed with Glyceria maritinia). A narrow strip 
on the left is occupied by G. Sd. ( Glyceria with Suceda maritima), 
while the upper portion of the grid is part of an area of Sd. G 
with SI. scattered through it. 
Fig. 80 shews that the surface of the channel is partly bare and 
consists partly of slipped masses of mud covered with SI. or SI. G. 
at a considerably lowel level than the general SI. G. plain, but 
considerably higher than the surface of bare mud, and with a few 
