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THE POPULAR SCIENCE MONTHLY. 



produces hairs. Half a dozen are early spring plants which flower 

 before the ants are roused from their winter sleep ; about the same 

 number are minute ground-plants to which hairs could be no protec- 

 tion ; three or four are night flowers ; there still remain a few to be 

 accounted for, which would have to be considered individually, but 

 probably the evidence is sufficiently complete to justify the general 

 inference. 



Lastly, I must not omit to mention the hairs which have a glandular 

 character. 



The next point to which I would call attention is the remarkable 

 manner in which certain forms repeat themselves. In some cases, 

 there seems much reason to suppose that one plant derives a substan- 

 tial advantage from resembling another. For instance, Chrysanthe- 

 mum ijiodorum, the scentless mayweed, very closely resembles the 

 camomile in leaves, flowers, and general habit. The latter species, 

 however, has a strong, bitter taste, which probably serves as a protec- 

 tion to it, and of which also, perhaps, the scentless mayweed may 

 share the advantage. These two species, however, are nearly allied 

 to one another, and I prefer, therefore, to take as an example of mim- 

 icry the stinging-nettle ( Urtica) and the common dead-nettle {Lamium 

 album). These two species belong to totally different families ; the 

 flowers are altogether unlike, but the general habit and the form of 

 the leaves are extremely similar. 



How close the similarity is may be seen by the illustration (Fig. 



21), taken from an excellent 

 photograph made for me by Mr. 

 Harman, of Bromley. The plants 

 on the right are true stinging- 

 nettles ; those on the left are the 

 white dead-nettle, one of which 

 is in flower. So close was the re- 

 semblance that, after getting the 

 photograph, I went back to the 

 spot on which they were growing 

 to assure myself that there was no 

 mistake. It can not be doubted 

 that the true nettle is protected by 

 its power of stinging ; and, that 

 being so, it is scarcely less clear that the dead-nettle must be protected 

 by its likeness to the other. Moreover, though I was fortunate in light- 

 ing on so good an illustration as that shown in the figure just when I 

 had the opportunity of photographing it, still every one must have ob- 

 served that the two species are very commonly found growing to- 

 gether. Assuming that the ancestor of the dead-nettle had leaves 

 possessing a faint resemblance to those of the true nettle, those in 

 which the likeness was greatest would have the best chance of survival, 



Fig. 21. 



