HONEY-DEW 25 



investigation of honey-dew was perhaps made by Reaumur, 

 who in the course of his studies on aphids observed that 

 these little insects discharge a sweet liquid from the intes- 

 tine. He remarked further that ants are fond of the 

 liquid, and protect or caress the aphids for the sake of it. 

 Linnaeus supposed that the aphids discharge the drops of 

 honey-dew from two tubes, which stand up from the 

 abdomen, and the statement has been repeated again and 

 again down to our own times. It appears to be altogether 

 baseless ; the tubes in question do indeed discharge drops 

 of viscid fluid, but these are defensive, and only serve to 

 annoy the many insects which come to prey upon aphids. 

 The proof of this is to be found in the pointing of the tubes 

 towards any threatening object, and the occasional 

 clogging of the face and jaws of the assailant with the 

 sticky secretion. Even after Reaumur had put forth his 

 clear and well-founded account of the origin of honey- 

 dew, the question was not finally disposed of. The belief 

 was strongly held, even by naturalists so recent and so 

 careful as Boussingault, Hooker and Darwin, that besides 

 the honey excreted by aphids there is a honey which 

 exudes from the sycamore. Several years ago this gene- 

 rally received belief was thoroughly tested by Biisgen in 

 his " Honey-dew ; biological studies on plants and aphids " 

 (Jena, 1891). He shows that the liquid is squirted out, 

 and falls not only on leaves, but on pieces of paper or 

 glass set below the places where aphids are feeding. The 

 drops form, not on that surface of a glass slip which is 

 in contact with the leaf, but on the surface which is turned 

 upwards, and appear suddenly, instead of gradually oozing 

 from pores. Biisgen described fully the process by which 

 aphids draw from the sycamore their supply of sugary 

 food. The proboscis is armed with long and extremely 

 flexible bristles, which seem to have the piercing powers 

 of the slenderest imaginable steel needles, and are able to 

 penetrate by winding passages the tissues of the leaf, until 

 they reach the vessels of the bast. Thus the nutritive 



