2o8 



SUPPLEMENT TO THE INTRODUCTION 



cation), I was at first more than surprised to hear of these experiments, for they seemed 

 entirely to overthrow a view which I had up to that time considered an established 

 oecological fact. But on careful consideration of these experiments, I came to the 

 conclusion that Plateau's inferences are not justified, and that another explanation is 

 permissible. Let us take the experiment made with Digitalis purpurea. Plateau cut 

 away not only the corolla-tube but also the style and stamens, till only a stump 

 I cm. long remained (see Fig. 80). Gaston Bonnier (' Les Nectaires,' 1879, p. 61) 

 observed many years ago that 'les abeilles continuent k visiter en meme nombre 

 les Digitales sur les pieds oil toutes les couronnes avaient ete enlevees.' Plateau's 

 experiments confirmed this observation, for the visitors of uninjured flowers (Bombus 

 terrester L. and Anthidium manicatum Z.) also sucked the mutilated ones, finding it 

 hard work to hold on while doing so — the resting-place presented by the complete 

 corolla being absent. 'Ainsi,' says Plateau, 'les hymenopteres visitent encore, et 



d'une fafon effective, les fieurs de Digitales 

 n'ayant plus ni leur couleur attractive, ni 

 des dimensions les rendant trfes visibles, ni 

 la forme que ces animaux ont coutume 

 d'utiliser pour parvenir aisement au nectar.' 

 But if we remember that a mutilated 

 flower is an open cup, containing nectar 

 which is constantly renewed from the 

 base of the flower — -where the nectar is 

 situated — we shall realize that this nectar 

 is freely displayed after removal of the 

 corolla, and therefore — being exposed to 

 the direct action of sunshine and wind — 

 must evaporate more quickly, give out a 

 stronger odour, and attract more strongly 

 than when it is hidden at the bottom of 

 a long corolla-tube. The visits of insects 

 to this exposed nectar-cup would therefore 

 be more numerous than those to the 

 uninjured flower, assuming that the corolla- 

 tube has no significance as a means of 

 attraction. No such observation, however, is found in Plateau's account, so that the 

 uselessness of the brightly coloured corolla for the purpose of attraction is not 

 proven. 



Plateau has also made similar experiments to those on Digitalis with Lobelia 

 Erinus, Oenothera biennis, Ipomoea purpurea, Delphinium Ajacis, and Antirrhinum 

 majus. As before he removed the conspicuous part as far as possible, and yet the 

 inconspicuous remnants — except in the case of Antirrhinum majus — received visits 

 from insects sometimes almost as frequently as the complete flowers. Plateau 

 explains that this is due to the fact that odour alone is the means of attraction. 

 In my opinion the mutilated flowers should here again have received more numerous 

 visits than the uninjured flowers, as in the former the odour of nectar must have 

 been stronger. Since the mutilated flowers were not visited so frequently as those 



Fig. 80. Digitalis purpurea^ L. (after 

 Plateau), a, complete flower; ^, mutilated 

 (lower. 



