FLOWERS AND INSECTS 
93 
class be recorded, a test of the general flower theory is obtained. A 
few examples may be quoted from a paper on the British flora ( Ann . of 
Bot. 1895). 
For each flower the number of species of insect-visitors of each class 
is recorded, and the totals thus obtained are given here : 
s 
A 
B' 
H 
I 
1 
o 
o 
£ 
1 
12 4 
12 43 
25 49 
This shows clearly, especially if calculated as percentages, the 
preferences exhibited by the various insect groups for the flowers whose 
tube-depths are best suited to them. The visitors to the flowers of class 
H are few in number, but by far more industrious than most of the 
visitors to class A. Class B' in Britain obtains the lion’s share of visits 
— this is explained by the abundance of Compositae in the flora. Many 
authors class together as allotropous all the shortest-tongued insects (i.e. 
short-tongued flies and all miscellaneous insects) and the corresponding 
flowers (classes Po, A, AB), as hemitropous those insects of medium- 
length tongues (short-tongued bees, long-tongued flies and all Lepi- 
doptera but the hawk-moths) and the flowers of classes B and B', and 
as eutropous the long-tongued bees and hawk- moths, and the flower- 
classes H and F. For a number of flowers observed in Britain the 
percentages were as follows : 
Class of 
p.c. of total 
p.c. of Eutr. 
p.c. of Hemitr. 
p.c. of Allotr. 
Flower 
insect- visits 
insect-visits 
insect- visits 
insect-visits 
Allotropous 
34*7 
5 ‘4 
21 '4 
487 
Hemitropous 
50*8 
54'6 
62*7 
43*0 
Eutropous 
H ’4 
40*0 
15*9 
8*3 
These percentage numbers give a measure (for the particular region 
and period of the year) of the attractiveness to insects of the different 
sorts of flowers. The first column shows the attractiveness to insects 
in general, the others the attractiveness to different groups. When a 
number in one of the latter columns exceeds the one in the first column, 
it shows a preference by that kind of insect for that kind of flower ; thus 
the hemitropous insects show a great preference for hemitropous flowers 
(62*7 — 50*8) and eutropous for eutropous flowers (40*0 — 14*4). 
When a comparison is made, upon the lines just indicated, between 
the floras of different countries, it is found that the proportions of the 
various classes differ a good deal. Thus in the extreme North of 
Europe eutropous insects are wanting, and there are few eutropous 
flowers. Those flowers that do occur are found either to have increased 
