HOW FLOWERS ATTRACT INSECTS 205 
Kienitz-Gerloff rightly makes the following remarks on this (Bot. Ztg., Ixvi, 
1896, pp. 123 and 124).—‘ Both premisses and conclusions are equally open to 
attack. For of course the covered dahlia heads could still attract animals by their 
odour—though this might not be perceptible to human beings—and to infer from 
this that the colour of uncovered flowers plays no part in attracting insects is the less 
justifiable as Plateau gives absolutely no comparative figures with regard to such 
visits, but only makes the very indefinite statement that insects flew to the covered 
flowers in the same way as to the uncovered, without hesitation and with equal 
eagerness. 
In the introductory words to the second part of his memoir, Plateau gives 
prominence to the fact that—his results being so diametrically opposed to existing 
views—he had continued his experiments on the question how flowers attract insects 
partly in his own garden, partly in the country, and partly in the Botanic Gardens at 
Ghent, where he had both repeated the experiments of other investigators and made 
entirely new ones. 
Of all Plateau’s researches those communicated in this second part appear to 
me to be the most important. In these he made use of flowers which had been 
rendered very inconspicuous by removal of the petals, or of the coloured part of the 
corolla, but which nevertheless received a very considerable number of insect visits. 
But before considering these researches in detail I should like first to deal with the 
other and less important experiments of this investigator. 
Plateau first repeated the experiments on dahlias with Heracleum Fischerii 
(Umbelliferae), by covering its umbels with rhubarb leaves. Yet within thirty 
minutes he observed three visits from Apis mellifica var. ligustica, two from other 
small bees, one from Calliphora vomitoria, and one from Phyllopertha horticola, 
followed in a further period of an hour and a half by twenty-five from Odynerus 
quadratus, ten from Prosopis communis, three from Calliphora vomitoria, and one 
from Musca domestica. 
In my opinion this only proves that the insects named are also attracted by 
odour, which has been disputed by none of the recent oecologists. No proof has 
been afforded that the attraction is only by odour, for no control experiments were 
made with uncovered umbels. From the fact that many insects (Apis, Andrena sp., 
Bombus sp., Megachile ericetorum, Pieris napi, Vanessa C. album, Eristalis, and the 
smaller Syrphidae) showed themselves zudifferent as regards the various colours of 
varieties of the same species, or of the species of the same genus, visiting without 
displaying preference the blue, white, purple, and rose-red flowers of Centaurea 
Cyanus, the red, purple, rose-red, orange, and white capitula of Dahlia variabilis, the 
purple, rose-red, and white capitula of Scabiosa atropurpurea, the red flowers of 
Linum grandiflorum and the blue ones of L. usitatissimum, Plateau concludes that the 
colours of flowers cannot play any part in the attraction of insects. He also cites 
the similar observations of other investigators, e.g. Darwin saw a humble-bee pass 
from a red Dictamnus Fraxinella to a white-flowered one, and another betake itself from 
one variety of Delphinium Consolida to another that was differently coloured, while 
much the same thing was noticed by Gaston Bonnier for the colour varieties of 
Althaea rosea, Digitalis purpurea, and Brassica oleracea, as well as by Errera and 
Gevaert for species of Pentstemon. 
