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THE NATURE BOOK 



to the height of fifteen feet, and is described 

 by Sir Joseph Hooker as having broad 

 glossy leaves covered with microscopic 

 hairs. The plant only seems to sting 

 violently in the autumn, but at that 

 time the strength of the poison is such 

 that people have suffered from its effects 

 for days. Moreover, at the time of its 

 greatest activity the plant gives off an 

 efflu\-ia which is so powerful that it causes 

 running from the eyes and nose. More 

 formidable still is the Urtica gigantea of 

 Australia, which grows into huge bushes 

 twenty feet or more in circumference. It 

 has been pointed out by Mr. Edward Step 

 that in the foliage of the Common Elm 

 very similar processes to the stinging 

 hairs of the Nettle are to be observed. 

 These are nothing like so formidable as 

 those of the Nettle, but are sufficiently 

 so to cause an annoying irritation to the 

 hands. Of course, the Elm is classed 

 with the same natural order as the Nettle. 

 It seems likely that these stinging hairs 

 serve a real purpose in protecting the 

 young growths of the Elm just at a time 

 when they would be most likely to be 

 damaged by grazing animals. 



A singular development is that to be 

 seen in the case of the Cuckoo Pint {Arum 

 maculatiini). In this case the tissue of the 



NETTLE STINGS (MAGNIFIED). 



foliage contains thousands of little crystal 

 needles (in addition to a certain acrid 

 poison) which stick into the lips, causing 

 an intolerable burning sensation. This 

 fact may be proved by anyone biting a 

 small portion of the leaf. Whether these 

 crystals are really a protective measure or 

 not, there is no doubt that the plant must 

 often be left alone on account of their 

 presence. The crystals are developed to 

 a much greater extent in the case of certain 

 tropical plants allied to the Arum. 



There is little doubt that the develop- 

 ment of sour and poisonous juices in 

 certain plants is valuable as a protective 

 measure. This is not invariably so, for 

 certain products such as the tannin in the 

 Oak are merely waste products — the out- 

 come of a definite chemical process. Still, 

 in the case of many species it is clear that 

 the plant derives a distinct advantage 

 from its offensive juice, and we can hardly 

 regard its presence as entirely accidental. 

 If we take the strong-tasting plants of 

 the countryside — the aromatic Mint, the 

 pungent Water Cress, the evil-smelling 

 Jack-in-the-hedge, to mention only three 

 examples — we shall assuredly find that 

 these species enjoy a comparative im- 

 munity from attack. True enough, as if 

 by way of retaliation, certain insect larvae 

 seem to have developed a special 

 fancy for some of these species ; 

 but, as a rule, the mild-tasting 

 vegetation is much more likely 

 to receive the attentions of 

 marauders. 



A very interesting problem 

 which arises in connection with 

 certain species of plants which 

 seem to be specially protected 

 is that of mimicry. The subject 

 is one concerning which we 

 have little positive knowledge, 

 yet some of the instances are 

 so striking that they cannot 

 well be ignored. On the face 

 of it there is, of course, nothing 

 preposterous in the conception 

 of plant mimicry, when we 

 have so well established a 

 theory on the same lines in the 

 case of animals. The common 

 Mint of our brooks, a particu- 

 larly attractive plant, which 

 sends up lusty shoots in the 



