304 



HUTCHINSON'S POPULAR BOTANY 



More formidable than airy of the protective weapons yet mentioned 

 are the barbed bristles which surround the buds on many of the Opuntias. 

 Each of these is a sort of compound fish-hook in miniature, and woe to 

 the unwary animal who pushes his nose against the smallest bunch of 

 them! The little hooks enter the tender flesh, and cause intolerable itching, 

 which is often succeeded by painful and, it may be, dangerous inflammation. 

 The tormenting bristles are easily driven deeper, but the backward-pointing 



barbs tear the flesh unmercifully 

 when any attempt is made to 

 withdraw them. One species, 

 Opuntia ficus-indica, better known 

 as the Prickly Pear, is abundantly 

 naturalized in the Mediterranean 

 area, where it forms inpenetrable 

 fences. Another species, Opuntia 

 feroXj is said by Schleiden to be 

 especially remarkable because of 

 the strength and size of its defen- 

 sive thorns. " Among the hairs 

 and smaller spines," he says, 

 " arise very long and thick spines, 

 in different form and number, 

 which give the best characters 

 for the determination of the 

 species. In some, these are so 

 hard and strong that they even 

 lame the wild asses which in- 

 cautiously wound themselves when 

 kicking off the spines to reach 

 the means to still their thirst. In 

 Opunlia tuna, which is the kind 

 most frequently used for hedges, 

 they are so large that even the 

 buffaloes are killed by the inflam- 

 mation following from these spines 

 running into their breasts. It was this species, also, which was planted 

 in a triple row as a boundary line between the English and French in the 

 island of St. Christopher." Fig. 366 represents a flowering branch of 

 Opuntia multiflora. 



No account of the protective armature of green leaves would be complete 

 without a reference to stinging hairs. The mention of these very remarkable 

 structures brings to mind the Common Nettle (Urtica dioica) a weed that is 

 known to every child. Let us take a peep through the microscope at one 

 of its stinging hairs, and try to realise what takes place when any rash 



FIG. 371. FLOWERING BRANCH or A ROSE SUR- 

 ROUNDED BY A BEDEGUAR GALL. 



The gall-fly and grub of same are shown in the corner of 

 drawing. 



