34 ATTRACTION OF INSECTS BY HONEY. [CHAP. 



conclusion that the secretion of honey is the result of 

 developmental energy, which afterwards concentrates 

 itself on the ovary. 



No doubt, however, seems any longer to exist that 

 Sprengel's view is right ; and that the true function of 

 honey is to attract insects, and thus to secure cross- 

 fertilisation. Thus, most of the Rosaceae are fertilised 

 by insects, and possess nectaries ; but, as Delpino has 

 pointed out, the genus Poterium is anemophilous, or 

 wind-fertilised, and possesses no honey. So also the 

 Maples are almost all fertilised by insects, and produce 

 honey ; but Acer negundo is anemophilous, and honey- 

 less. Again, among the Polygonaceae, some species are 

 insect-fertilised and melliferous, while, on the other 

 hand, certain genera, Rumex and Oxyria, have no 

 honey, and are fertilised by the wind. At first sight 

 it might appear an objection to this view, and one 

 reason perhaps why the earlier botanists missed the 

 true explanation, may have been the fact, that some 

 plants secrete honey ou other parts than the flowers. 

 Belt and Delpino have, I think, suggested the true 

 function of these extra floral nectaries. 1 The former 

 of these excellent observers describes a South 

 American species of Acacia : this tree, if unprotected, 

 is apt to be stripped of the leaves by a leaf-cutting 

 ant, which uses them, not directly for food, but, 

 according to Mr. Belt, to grow mushrooms on. The 

 Acacia, however, bears hollow thorns, while each leaf- 

 let produces honey in a crater-formed gland at the 



1 I, by no means, however, -wish to suggest that we as yet fully under- 

 stand the facts. For instance, the use of the nectary at the base of tb.2 

 leaf of the Fern is still quite unexplained. 



