138 MR. MILLER CHRISTY ON THE 
Ostenfeldt *, the Primrose has long been known to occur, and is apparently 
native, on rock-ledges near Trödun, on Sandö. Here, however, certain 
insects which might conceivably pollinate it are known to occur; for Neilsen 
says? that at least one species of bee (? Bombus sp.), a few Noctuidæ and 
Geometridz, and a single individual of Vanessa cardui have been observed 
on the islands. 
Yet, however probable—indeed, inevitable—this hypothesis may be, it is, 
for several reasons, very difficult to prove its truth conclusively. Thus, it 
is obviously far from easy—in fact, practically impossible—to follow closely 
in the dark the movements of any small flying creature ; and, in the case of 
moths, there is the further difficulty that many of them fly at certain hours 
and for a short period (say, an hour or so) only. To make sure of seeing 
them at all, therefore, one must first ascertain the proper hour to watch, and 
then to watch at that particular hour; which is not always possible. 
Mr. Dallman, with the aid of an electric flash-lamp, was unable to detect any 
flying insect whatever in the act of visiting a Primrose f. 
It is for these reasons, probably, that Darwin's hypothesis on the point, 
though advanced as far back as sixty years ago and hotly discussed exer since, 
remains to this day neither proved nor disproved. Probably, indeed, it is 
quite incapable of absolute proof by means of ordinary observation. It ought, 
however, to be provable or disprovable, without great difficulty, by means of 
direct experiment; and I suggest that such be undertaken by some competent 
observer who happens to possess suitable opportunities. 
There are two lines, along either or both of which (it seems to me) 
experiment might be carried out :— 
First, some sticky substance, like bird-lime, might be placed in the evening 
in the bottom of the corolla-tube of a number of flowers, with a view to 
catehing by the proboscis, and retaining tili the morning, any insect which 
had visited the flowers during the night$. This method, if successful, would, 
of course, show the actual species of moth concerned. 
Or, a number of plants (say, fifty or a hundred), all growing together in 
natural conditions (preferably in a wood), might be selected for experiment. 
Just before flowering, all might be * covered " (by the means usually adopted 
for preventing insects from obtaining access to and pollinating flowers) and 
so remain till all or most of the plants were in full flower. Then one half of 
* ‘Botany of the Faroes,’ p. 50 (1901-8). 
t Op. cit. p. 1066. 
I Journ. of Botany, lix. (1921), p. 344. | 
§ I tried this with ordinary bird-lime as long ago as 1882, but with so li tle success 
(probably because I placed the bird-lime on the limb of the corolla, instead of in the tube) 
that I never repeated the attempt. 
