THE YOUNG 



NATURALIST. 



how a few external defences such as 

 hairs or prickles will determine them 

 in choosing a meal. Against such 

 enemies the tough, leathery epidermis 

 of various leaves, such as the ivy, must 

 stand the plant in good stead, and the 

 firm, corky bark of trees and shrubs 

 be an impervious coat of armour. 

 Viewed in this broad sense, it may be 

 said that no plant is utterly defenceless; 

 and to admit it were so, would involve 

 that in the constant struggle for ex- 

 istence, in which the weakest must 

 invariably succumb, it would long ere 

 now have become extinct. 



When we consider the secondary or 

 special means of defence in plants we 

 see such an immense variety of devices, 

 organs so modified and arranged to 

 serve a specific purpose, that again it 

 is difficult to find a plant which is not 

 armed at some point to resist some 

 insiduous foe. What we may call 

 these local defences are usually so 

 placed as to protect the flower from 

 the invasions and ravages of insect 

 marauders who would rob the blossom 

 of its stores of nectar without any 

 compensating advantage to the plant. 

 Most formidable of these are ants, 

 whose love of honey is proverbial, and 

 many special devices are framed to 

 prevent their access to the flower. 

 Thus the hairs which clothe the stems 

 of so many plants are usually found 

 to point downwards, forming an im- 

 penetrable barrier to any small crawl- 



ing insect that attempts to creep 

 upwards. Observe the hairs on the 

 hemp nettles (Galeopsis), or in many 

 umbellifers, or grasses such as the 

 wood brome-grass. Even if these ob- 

 stacles should be surmounted, or in 

 many cases where the stems are smooth, 

 the flower itself is protected by hairs 

 and prickles, as in the moss-rose; 

 either the calyx itself is hairy, or, as 

 in composite flowers, the scales of the 

 involucre bristle with spines and 

 barbed hooks, as in the thistles and 

 burdocks ; or they form a circling 

 stockade, as in scabiosa, astrantia, or 

 eryngium. The angles formed by the 

 outspread flower must also be difficult 

 to clamber over by an ascending insect. 

 Again, the very peculiar shape of the 

 corolla itself is often a protection, as 

 in the snapdragon, where it is firmly 

 closed against the admission of small 

 insects, requiring the strength of a 

 large humble-bee to force an entrance. 

 In many cases the interior of the 

 corolla is fringed with hairs, forming 

 a barricade against the intrusion of 

 unbidden guests. Observe the throat 

 of the various bell-shaped flowers, or 

 those of the common garden nastur- 

 tium. But it would be tedious to 

 enumerate all these special contri- 

 vances, as every plant is furnished 

 with some peculiar protection. One 

 very marked and effective defence 

 against such intruders is the viscid 

 gum exuded by various plants. This 



