MAPPING AS AN ECOLOGICAL INSTRUMENT. 
733 
high and low ground, instead of being confined to the hummocks. 
In 1909 the population of Salicornia had decreased to a 
remarkable extent, the distribution being far more regular than 
before. The Suceda maritima, on the- other hand, showed a 
corresponding increase in number, the whole area being densely 
colonised by both purple and green types. 
Such charts give a graphic picture of the fact that owing to 
certain ecological changes an area which initially supported 
apple green Salicornia in the hollow and Suceda maritima on 
the hummocks changed its population so much in four years 
that hummocks and hollow alike were filled with dense masses 
of Suceda maratima , the Salicornia taking only a secondary 
place. 
Charts and maps provide a most useful check to observations 
made by the eye. Where several species occur in association 
it is often difficult to make a fair estimate of their relative 
dominance, as the difference in habit is apt to bias one’s 
judgment. For instance, if Suceda maritima and Salicornia 
europcea are growing together, the Suceda will often give a 
false impression of dominance owing to its bushy habit, as 
a few bushy Sucedas make more impression on the eye than a 
far greater number of the straight, little-branched Salicornias. 
To sum up, it can easily be seen that the uses and applications 
of mapping as a scientific instrument are many and varied. 
With certain main principles underlying the whole process, 
there is yet scope for the play of much individuality on the 
part of the investigator. A few essential points must be 
observed — the areas to be mapped need careful selection, while 
the methods adopted should be as simple as is consistent with 
the attainment of the end desired. Given these essentials, it 
is certain that the usefulness of mapping has not yet been 
fully recognised, and that as time goes on extended applications 
of the system will develop. 
