SPINES AND PRICKLES BRISTLES AND HAIRS 101 



the plant. If the student make out a table for himself something 

 like the following, he will be able to assign in each case the prickle 

 to its particular origin. 



BRISTLES AND STINGING HAIRS 



Many plants such as borage, comfrey, and nettle have peculiarly 

 formed structures on their stems and leaves. A very little trouble 

 and the use of a microscope will enable the student to find out the 

 nature of the weapons of defence. 



It is a matter of common knowledge that a nettle grasped by 

 the stem and stroked from below does not sting, while any attempt 

 to seize it from the top will result in the offender being stung. What 

 is the cause of this ? It is again often said that if a nettle is grasped 

 strongly no pain will be felt. Is this so ? If so, why ? 



Lastly, reference must be made to a non-British plant so common 

 in our greenhouses, the cactus. Unless the student is a botanist, he 

 will almost certainly fail at first sight to say what part of the plant 



