THE HAIRS 



OF NETTLES 



WWES you l)rush against a net- 

 tle, \'ou are stung by a \'ery 

 sim])le weajjon. The plant 

 has many fine hairs, each of 

 which is hollow and filled with an 

 albuminoid liquid under i^ressure. 

 Touch breaks oft' the point of the hair 

 and leaves, in effect, a tiny hypodermic 

 needle, which injects its contents under 

 the skin, i)ro(lucing a burning sensa- 

 tion that cannot be overlooked. 



These stinging hairs, while simple, 

 are of a very si)ecialized character, and 

 at first sight one would feel no doubt 

 that they had some useful part in the 

 ]:)lant's life. Otherwise, it might be 

 argued, they would not exist. 



ARE THEY USEFUL? 



But recent students have strongly 

 questioned this attitude toward nature. 

 In their Text-book of Botany (ii, vS77) 

 Coulter, Barnes and Cowles say: "No- 

 where in plants is there an organ more 

 clearly fitted for a definite function than 

 are stinging hairs, yet there is no evi- 

 dence that they are of any special ad- 

 vantage to the plant possessing them. 

 Nothing is known concerning the 

 factors underlying their development, 

 since they neither vary appreciably nor 

 grade obviously into other sorts of 

 hairs." 



CAN'XOT HI-; DISCARDED 



Plants have numerous kinds of hairs, 

 and in some cases it has been found 

 that they are of advantage as a pro- 

 tection from the cold or heat, or to 

 l)re\'ent excessive evaporation of npis- 

 ture. In other cases they do not seem 

 to l)e of any value to the i)lant, and may 

 l)erha])S exist merely as by-])roducts of 

 some i)art of the ])lant's evolution. It 

 is likely, the authors above-mentioned 

 think, "that most such hairs are of 

 little or no advantage. The idea should 

 It is a sinKlc clonpicd tdl, the wall.s \^^^ abandoned that plants have the 



of which arc hardcncrl with sihca. , ,• .„„^ i ,^^.,„„.. fi,^« o.-.. ,-,r^^• /^f 



PhotomicroKraph hv |..hn llnwanl P«^^'^''^ ^o discard organs that are not of 



Paine. (Fij,'. 14.) nsc. 



240 



A STIN(;iN(. II \IK 



