294 Matthews .— The Distribution of certain 
It has already been suggested that plants may reach the Channel or 
Thames region by dispersal along a circuitous route, say through the 
Peninsula or the Ouse, as well as by direct migration. In the course of 
time, as a result of the meeting of different migrations, the intermediate 
districts, Thames and Channel, would attain a larger flora than the areas at 
the extremities of the region, assuming that plants are arriving in approxi¬ 
mately equal numbers and spreading at roughly equal rates—conditions not 
likely to be fulfilled in nature. But even an approximation to such con¬ 
ditions would produce an average result in which the working out of the 
Age and Area principle would be obscured if applied to the total flora. In 
the present case, in fact, we have a group of 233 species distributed through 
the four districts of the area under consideration as follows: 
75 occupy one district; 
43 occupy two districts ; 
62 occupy three districts ; 
53 occupy four districts. 
The figures are not particularly suggestive of ‘Age and Area’, yet 
when they are disentangled the applicability of the law becomes more 
apparent. The rarest species (99) are distributed as follows: 
67 occupy one district; 
19 occupy two districts ; 
11 occupy three districts ; 
2 occupy four districts. 
Thus the rare species are seen to follow the general law much more closely. 
Whatever the cause of the rarity, if these species are the result of different 
invasions, the admixture in any one district due to migration from different 
directions will be relatively small. We should expect, then, that the general 
principle should apply to any particular invasion, although it has to be 
noted that the numbers involved become much smaller. That this is so 
has already been indicated in the results shown in Table II, but the facts 
may now be expressed in the usual ‘ Age and Area ’ way. They are given 
in Table IV. 
Occupying 
41 Peninsula 
Table IV. 
39 Channel 
29 Thames 
37 Ouse 
species. 
species. 
species. 
species. 
One district 
21 
14 
11 
21 
Two districts 
11 
13 
7 
7 
Three districts 
n 
4 
10 
9 
7 
2 
Four districts 
2 
2 
2 
The results 
agree fairly well with Willis’s 
hypothesis. 
When a specie 
occurs throughout the whole region it is, of course, not easy to determine to 
