HOW FLOWERS ATTRACT INSECTS 207 



Cerinthe minor — they are kept away from natural flowers that have already been 

 visited. Plateau on several occasions observed ' inspection flights ' of certain insects, 

 which were to be regarded as undertaken for the purpose of making observations, 

 and not as ' smellings ' at the artificial flowers in order to test them. For example, 

 a bee on Saxifraga umbrosa undertook ' un vol ascendant d'inspection devant une des 

 grappes imit6es,'and again, 'Une seule Melanostoma mellina a vole un instant devant 

 la grappe mielMe.' Plateau remarks with regard to Lathyrus latifolius that bees of 

 the species Megachile ericetorum paused a moment in their flight on encountering 

 the artificial flowers, but never settled upon them — ' Les insectes ont tournoye un 

 moment, dans un but d'examen, autour des grappes artificielles, sans, du reste, 

 jamais tenter d'entrer dans une de ces fleurs.' 



Only the Muscidae — long ago described as ' stupid ' by Ch. K. Sprengel — 

 now and then allow themselves to be deceived, or go after honey which has been 

 hidden in artificial flowers. Artificial apple-blossoms, for instance, were visited by 

 Calliphora and Musca, and a specimen of Calliphora crept into an imitation flower of 

 Digitalis purpurea into which honey had been put. 



Plateau himself thought that there might possibly be slight differences between 

 the colours of artificial and natural flowers, deterring insects from visiting the former. 

 He therefore made artificial flowers by folding up green foliage leaves and fixing in 

 them a small sponge saturated with honey. Apis, Musca domestica, Calliphora 

 vomitoria, Sarcophaga carnaria, Lucilia caesar, Odynerus quadratus, and Bombus 

 terrester at once made their appearance for the purpose of enjoying the honey. 

 As already pointed out, there is nothing remarkable about this, for it is well known 

 that insects are strongly attracted by the odour of honey. 



But for other odours the results are quite different. When Plateau added to 

 honey a drop of essence of lavender, thyme, sage, mint, orange, or bergamot, there 

 were no insect visits. Even when he employed very dilute solutions of these 

 odorous substances but few insects were attracted. The following inferences can 

 be drawn from these facts : — 



1 . The essences employed have a relatively small attractive power. 



2. A few of them (mint) are even repellent. 



3. Only the essences of thyme and sage are feebly attractive. 



From these experiments it follows that solutions of odoriferous plant extracts, 

 which according to Plateau ought to attract insects, do not do so. His theory is 

 therefore refuted by his own experiments. 



Plateau further adduces the case of numerous green, greenish, brown, or brownish 

 flowers or inflorescences which are visited and pollinated by insects, but this merely 

 proves that insects are guided to inconspicuous flowers by odour, not that colour is 

 of no importance. Plateau has not compared the frequency of insect visits to 

 inconspicuous and conspicuous flowers of the same size, and it is only experiments 

 of this kind which can help to settle the point at issue. 



As already mentioned, those experiments of Plateau in which he prepared 

 inconspicuous mutilated flowers by reinoving the petals or the coloured part of the corolla 

 — with the result that even then they received a great many insect visits — demand full 

 consideration. As mentioned in my ' Vorlaufige Mitteilung' (i.e. Preliminary Communi- 



