Ch. XII.] USE OF HOXEY-SECKETING GLANDS. 225 



every young leaf and every flower-bud had a few on 

 them. They did not sting, but attacked and bit my 

 ringer when I touched the plant. I have no doubt that 

 the primary object of these honey- glands was to attract 

 the ants, and keep them about the most tender and 

 vulnerable parts of the plant, to prevent them being 

 injured ; and I further believe that one of the principal 

 enemies that they serve to guard against in tropical 

 America is the leaf-cutting ant, as I have noticed that 

 the latter are very much afraid of the small black ants. 



On the third year after I had noticed the attendance 

 of the ants on my passion-flower, I found that the glands 

 were not so well looked after as before, and soon dis- 

 covered that a number of scale-insects had established 

 themselves on the stems, and that the ants had in a 

 great measure transferred their attentions to them. An 

 ant would stand over a scale-insect and stroke it alter- 

 nately on each side with its antenn.se, whereupon every 

 now and then a clear drop of honey would exude from a 

 pore on the back of the scale-insect and be imbibed by 

 the ant. Here it was clear that the scale-insect was 

 competing successfully with the leaves and sepals for the 

 attendance and protection of the ants, and was suc- 

 cessful either through the fluid it furnished being more 

 attractive or more abundant. I have, from these facts, 

 been led to the conclusion that the use of honey- secreting 

 glands in plants is to attract insects that will protect the 

 flower-buds and leaves from being injured by herbivorous 

 insects and mammals ; but I do not mean to infer tha+ 

 this is the use of all glands, for many of the small appen- 

 dicular bodies, called " glands ' : by botanists, do not 

 secrete honey. The common dog-rose of England is fur- 



Q 



