2o6 SUPPLEMENT TO THE INTRODUCTION 



In none of these cases is Plateau justified in the general inference that the 

 colours of flowers play no part in attracting insects. The only conclusion to be 

 drawn is that in flowers of {he same shape the colour is a matter of indifference to the 

 visitors, and that these possess an exceedingly well-developed sense of form. The 

 honey-bee, as is well known, and as Hermann Miiller repeatedly points out, after once 

 making a beginning keeps with great constancy to one species of flower, sucking this 

 alone to the exclusion of all others which may be present. And that in this it is not 

 guided by odour but hy colour and form appears from the circumstance that it often 

 makes indiscriminate visits in the case of flowers that are similarly formed though of 

 different species, e.g. Sinapis arvensis and Raphanus Raphanistrum, which cannot, 

 however, be supposed to possess the same odour. 



The fact that according to Plateau's further experiments very conspicuous 

 flowers, which as a rule receive few visitors (e.g. Pelargonium zonale Willd., Phlox 

 paniculata Z., Anemone japonica Sieb. el Luce, Convolvulus sepium Z.), attract large 

 numbers when honey is put upon them, only proves that the odour of honey exercises 

 a great power of attraction upon insects, which has long been known. It is only 

 necessary to place honey anywhere to secure the immediate appearance of numerous 

 insects which are fond of it. 



In a similar way may be explained Plateau's numerous experiments on anemo- 

 philous flowers, by adding diluted honey to which numerous insects were attracted. 

 When Plateau further proved that insect visits ceased after removal of the nectar-pro- 

 ducing structures (of dahlias), but began again when nectar was reintroduced — Bombus, 

 Megachile, and Vespa making their appearance — he confirmed the well-known fact 

 that insects can accurately distinguish between the nectarless and nectar-yielding 

 flowers of a given species. On this point Hermann Miiller writes as follows 

 ('Weitere Beobachtungen,' III, p. 13):— -' Honey-bees and humble-bees when 

 despoiling Cerinthe minor display their great skill in recognizing small differences 

 between flowers. Some of the flowers that have been visited, and in which the pyramid 

 of stamens is pressed apart at the apex, they fly past without touching, others they 

 touch in passing only to leave again immediately. They fly with extended proboscis, 

 humming as they go, and steadily searching from flower to flower, till they have 

 found one filled with nectar.' From this it appears that insects can see extremely 

 well at a short distance, and that they are led by sight to the flowers they visit. 



The recognition of artificial flowers by insects obviously depends upon this 

 appreciation of very minute differences, and involves both sight and smell. It is 

 accordingly not to be wondered at that insects should not have visited the artificial 

 flowers of Ribes sanguineum Persh., Persica vulgaris Mill., Cerasus vulgaris Mill., 

 Myosotis alpestris Schm., Pyrus Malus L., Saxifraga umbrosa Z., Digitalis purpurea 

 Z., and Lathyrus latifolius Z., which were placed by Plateau among natural flowers 

 of the same species, but left them unheeded, even when provided with honey. 

 Though these artificial flowers may seem very realistic to human eyes, yet insects are 

 not to be deceived, for the surface of such flowers appears quite different on close 

 inspection from that of natural ones, and their odour — due to the materials of which 

 they are made — is easily perceived by insects, though perhaps not by us. 



Two causes, one due to sight, the other to smell, prevent insects from visiting 

 artificial flowers, just as^according to the observations of Hermann MuUer on 



