Methods of Surveying Vegetation. 233 
hand, and in the bottom left hand corner of the square. Of vege¬ 
tation-covering, the right and left hand portions bear the Scilicornia 
herbacea-Glyceria maritima association (SI. G.), whilst on the middle 
parts grows a turf of Suez da maritima and Glycerin with a scattering 
of Snlicoruia (Sd. G. + SI.) The central Sd. G. is bordered on the 
right by a narrow belt of SI. G. and again between this and the 
Sd. G. of the extreme right there is a second narrow belt in which 
Suczda is dominant in association with Glycerin and Snlicornin 
(Sd. + G + SI.) 
The notes which accompany this map shew that associations in 
which Suczdn is a dominant or a co-dominant lie at a slightly higher 
level than than those in which Snlicornin plays a corresponding role. 
Were we in a position to add-some dozen spot-levels to this map 
the relation of the plant-associations to differences in level would 
be evident. This important feature, however, is fully illustrated in 
the case of the “gridiron” described below. 
The Gridiron Method. 
The “ Gridiron ” method is essentially an adaptation of the 
“ method of squares ” to a survey of vegetation in greater detail. 
It is suitable for use where the physical features, with which the 
different plant formations are correlated, exhibit definite variation 
within quite short distances. The scale used in the present 
instance was ^, a square “gridiron” having a side of 25 feet 
being plotted on a square of paper having a side of 5 inches, so 
that the tenth of an inch rulings on the paper used (see above) 
correspond to distances of 6 inches on the ground. This scale 
allows the insertion of as much detail as is ever likely to be re¬ 
quired in mapping vegetation; it is quite easy, for instance, to put 
in the positions by means of symbols of individual scattered plants 
of species not forming a constituent of a continuous plant- 
carpet (e.g. Obione portulncoides and Snlicornin rndienns in the 
specimens given below, Fig. 80). 
The method of procedure is as follows. The 25-foot square is 
first pegged out, and tapes are laid round its sides. Four 25-foot 
tapes are then laid across the square at intervals of 5-feet, so as 
to divide the square into 5 strips, each measuring 25 X 5 feet. 
Thus the “ gridiron ” is formed (Fig. 79). The tapes corresponding 
to the bars of the gridiron should run across the greatest number of 
physical features and association boundaries to be mapped, rather 
than parallel to them. The “ bars ” of the gridiron of course 
