21 I 
and the Problem of Endemism . 
range but are confined to Ceylon and adjacent Peninsular India; and (3) those 
which occupy a still wider area. The following table shows the composition, 
as to growth habit, of these three classes : 1 
Table I. 
Trees %. 
Shrubs %. 
Herbs %. 
Endemic 
45 
33 
22 
Ceylon-P. I. 
2 5 
35 
40 
Wide 
20 
26 
54 
It is evident that among the endemics, trees possess more than twice as 
many species as herbs ; in the Ceylon-Peninsular Indian class only five- 
eighths as many, and among the ‘Wides’ less than two-fifths as many. 
Shrubs, it will be noticed, are in every case intermediate between trees 
and herbs. 
Still more convincing is a study of the relative areas occupied by 
members of the three growth forms in Ceylon itself. Trimen divides the 
species into six classes of progressively greater rarity, using ‘ Common ’ in 
the sense of widespread and ‘ Rare ’ in the sense of restricted in range. These 
classes he designates as Very Common, Common, Rather Common, Rather 
Rare, Rare, and Very Rare. The percentage of trees, shrubs, and herbs 
in each class is shown in Table II. 1 (Herbs comprise 37 per cent, of the 
dicotyledonous flora as a whole.) 
Table II. 
Trees %. 
Shrubs % . 
Herbs %. 
Very Common 
11 
29 
60 
Common 
28 
28 
44 
Rather Common 
29 
27 
44 
Rather Rare 
35 
30 
35 
Rare 
3i 
33 
36 
Very Rare 
30 
33 
37 
Here again it is evident that herbs preponderate among the ‘ Common * 
species but form a much smaller portion of the ‘ Rare ’ ones, whereas with 
trees just the reverse is the case. Figures like the ones cited in these two 
tables could be multiplied almost indefinitely for other floras. Habit of 
growth is clearly an important factor in determining the area occupied by 
a species. 
A recognition of the fact that there are many effective influences other 
than age which decide what a plant’s range shall be is not the only difficulty 
which the 4 age and area ’ hypothesis must meet, for a strict application of 
it leads to conclusions which are not easy to defend. In the floras of Ceylon 
and New Zealand, for example, the endemic species have, in the great 
majority of cases, a much narrower range than do the non-endemic species ; 
and this fact necessarily causes Dr. Willis to conclude that the endemic 
1 Dicotyledons alone considered. 
