THE PLANT AND ITS ENEMIES 



999 



gathered, commencing with the speci- 

 mens from the lower branches, which are 

 fully armed, and ending with those from 

 the uppermost shoots, which are quite 

 destitute of any prickles. As in the case 

 of the thorny plants, it is to be noticed 

 that prickles are produced in the greatest 

 abundance when the specimen is having 

 a hard time of it. Thus Briar Roses 

 which have been cut back in liedges send 

 up their fresh shoots abundantly supplied 

 with prickles. 



Closely alHed to the prickles are the 

 various hairy appendages which are so 

 often distributed over the foliage of plants. 

 The leaves of the Orange Hawkweed, and 

 even the flower stems, are covered with 

 stiff black hairs. Plants protected in this 

 manner are not subject to the attacks of 

 insect larvae, slugs or snails, as would be 

 the case if the fohage were perfectly plain. 

 Similarly, grazing animals are less inclined 

 to regale themselves on leaves which are 

 thicklv covered with bristles. 



There must be few people who have 

 not suffered at one time or another 

 through coming into contact with the 

 stinging hairs of the Nettle. Under the 

 microscope it is seen that these stings 

 consist of a long tapering cell, rising 

 from a cushion-like base. The point of 

 the hairs is easily broken, owing to the 

 cell wall being very thin. When the hair 

 comes in contact with any object which 

 the ape.x can pierce, a slight wound is 

 made, and at the same time the upper 

 part of the bristle breaks, allowing the 

 fluid which the cell contains to escape into 

 the opening. The poison, consisting as it 

 does of formic acid and a property known 

 as enzyme, is of a peculiarly irritating 

 nature — as most people will have e.\- 

 perienced to their cost. 



Far more formidable, however, are the 

 stings of certain exotic species, one of 

 which, the great Shrubby Nettle {Urtica 

 crenulata) of Northern India, is a really 

 formidable plant. This species attains 



INK-BOTTLE OR URN-SHAPED FLOWER OF THE WHORTLEBERRY. ESPECIALLY 

 DESIGNED TO EXCLUDE CREEPING INSECTS. 



