POLLINATION OF THE BRITISH PRIMULAS. 139 
the plants might be exposed just after dusk and re-covered just before 
sunrise, while the other half might be exposed just before sunrise and 
re-covered just before dusk. This might be continued for (say) three days or 
nights, after which all the plants should remain covered permanently until 
the time when any seed they may have set should have ripened. If, then, 
the plants were examined and it was found that those which had been 
exposed by night only had fruited freely, while those exposed by day only 
had not, we should have good evidence that the plants are pollinated normally 
by night-flying moths; or, if the converse were found to be the case, we 
should know that the large-tongued bees-and butterflies which are known 
to visit the flowers by day suffice to pollinate them adequately, though this 
appears at present to be impossible, owing to the fewness of their visits. 
But this method, though it might prove conclusively that the flowers are 
pollinated normally by night-flying moths, would not show the particular 
species by which this is effected. 
For invaluable advice and help, I desire to thank many friends, most of 
whom have already been named ; not least am I indebted to Dr. James 
Waterston, F.E.S., who has kindly identified the specimens in a small 
collection of bees taken by myself in the act of visiting Primula flowers, and 
Mr. Charles Nicholson, F.E.S., who has been good enough to read through 
my proofs. 
29th August, 1922. 
