METHODS OF RESEARCH IN FLOWER POLLINATION 199 
periods of time, by still further dividing the insect groups, and by increasing the 
number of observations. 
The first of MacLeod’s graphic tables is reproduced, where each ordinate 
represents one of the seven flower classes (An, £, EC, C, S, H, L), while abcde/g 
is the general insect line for the month of June in the Alps—below the limit of trees— 
and aSyée¢n is the Diptera line. 
For complete understanding of the law regulating the visits of insects to flowers 
the statistical observations that have hitherto been made in flower pollination are not 
sufficient, and full knowledge of this 
law will only become possible when pant Be BOC, So AE 
numerous investigators take part in 
the work. Besides which many other 90 
related matters require more thorough 
study, e.g. the determination of the 80 
distribution of the sexes in different 
districts, the mechanisms of many ae 
flowers, and so forth. These pro- 
; 60 
blems, however, cannot be solved till 
such investigations have been sys- 50 
tematically made in as many small, 
well-defined areas as possible. 40 
When only occasional observa- 
tions are made on flower pollination, 30 
it will appear as if insect visits were 
18 re 
often very rare, even in the case of | a0 Pan “Ye 2 
the larger and more conspicuous 10 Q /|> Bod ee) 
flowers. As a matter of fact we cannot a er g 
calculate on seeing numerous insects ora. /] 
visiting flowers in rainy or even dull Fic. 77. Graphic representation of the visits of Diptera 
weather, or in strong wind, and under ‘© various classes of flowers in the month of June (after 
2 2 J. MacLeod), reduced one-fourth. adcdefg, general insect 
such circumstances only occasional line for the month of June in the Alps below the limit of 
: : : trees; aBy5e¢y, Diptera line. [The symbols for the flower 
stragglers will be noticed. Even in classes used in this translation have been substituted for 
warm, quiet weather there is frequently %4, 42, 3, 3, 4, F employed by MacLeod.—TR.] 
no abundance of flower guests to be 
seen, and it then becomes necessary to patiently stay in one place and not wander 
aimlessly about. ‘One must not be annoyed,’ says the great Sprengel (‘ Entd. Geh.,’ 
p- 23), ‘at having to spend a long time near a flowering plant, and at having often 
to repeat the same observations on any species of flower, for it is not always visited 
forthwith by the particular insect which is designed to fertilize it.’ As a rule patience 
will be rewarded, the proper insects putting in an appearance at last, even when the 
plant under observation stands alone. In the study of flower pollination it is neces- 
sary always and everywhere to be ready at a moment’s notice to make observations. 
It should therefore be a rule never to go out without apparatus for capturing insects, 
and always to carry about cases for preserving captured specimens. Immediately 
after the sun has dried up the dews of night from the flowers the insects come forth 
from their night’s quarters to make their visits, and the student of flower pollination 
