SOME COMMON OBJECTS 49 



course — the general study of plant-hairs, which is a 

 very fruitful subject. 



Putting on a glove, or otherwise protecting the 

 hand, we secure and take home a plant of the 

 stinging-nettle. We first examine it with the 

 pocket lens, which shows that the stinging hairs are 

 scattered over stem and leaves. But we desire to 

 observe the structure of these interesting hairs, and 

 to do this must use the compound microscope. 

 With a sharp knife we cut away a very thin portion 

 of the cuticle or " skin " of the stem, with hairs 

 attached. This portion is placed between two glass 

 slips, and examined -with a 1-inch objective. If the 

 object is properly manipulated we can now see that 

 each hair is really a flinty needle channelled through 

 its centre, and having at its apex a tiny ball of flint 

 closing the tube. At the base is a poison sac, or 

 bag, containing the irritating fluid. We soon gather 

 that the sting we feel is due to this fluid being forced 

 into our skin through the centre of the needle. In 

 touching these stinging hairs as they are on the 

 living plants we break away the little ball closing 

 the tube at the apex, and the slight pressure of the 

 touch is sufficient to enable the fluid to be forced up 

 the channel into the skin, which is already pene- 

 trated by the sharp needle. The sting of the nettle 

 is a natural hypodermic syringe. We may prove 

 the flinty character of the hair by placing it upon a 

 a small piece of platinum, and burning it over a 

 spirit lamp. The heat will destroy all organic 

 matter, but leave the flinty needle intact. 



The study of plant-hairs can readily be extended 

 and become thoroughly fascinating. Without call- 



7 



