HONEY-DEW 173 



the experiment in person), as in many other instances we 

 know that conspicuously-coloured insects advertise their 

 nastiness, as it were, to the birds by their own integuments, 

 and so escape being eaten in mistake for any of their less 

 protected relatives. 



On the other hand, it seems pretty clear that certain 

 plants have efficiently armed themselves against the 

 aphides, in turn, by secreting bitter or otherwise un- 

 pleasant juices. So far as I can discover, the little 

 plunderers seldom touch the pungent ' nasturtiums ' or 

 tropseolums of our flower-gardens, even when these grow 

 side by side with other plants on which the aphides are 

 swarming. Often, indeed, I find winged forms upon the 

 leaf-stem of a nasturtium, having come there evidently in 

 hopes of starting a new colony ; but usually in a dead or 

 dying condition the pungent juice seems to have poisoned 

 them. So, too, spinach and lettuce may be covered with 

 blight, while the bitter spurges, the woolly-leaved arabis, 

 and the strong-scented thyme close by are utterly un- 

 touched. Plants seem to have acquired all these devices, 

 such as close networks of hair upon the leaves, strong 

 essences, bitter or pungent juices, and poisonous principles, 

 mainly as deterrents for insect enemies, of which cater- 

 pillars and plant-lice are by far the most destructive. It 

 would be unpardonable, of course, to write about honey- 

 dew without mentioning tobacco; and I may add paren- 

 thetically that aphides are determined anti-tobacconists, 

 nicotine, in fact, being a deadly poison to them. Smoking 

 with tobacco, or sprinkling with tobacco- water, are familiar 

 modes of getting rid of the unwelcome intruders in gardens. 

 Doubtless this peculiar property of the tobacco plant has 

 been developed as a prophylactic against insect enemies : 

 and if so, we may perhaps owe the weed itself, as a 

 smokable leaf, to the little aphides. Granting this hypo- 



