50 THE STOKY OF THE PLANTS. 



against it, many plants produce leaves which are 

 prickly, or stinging, or otherwise unpleasant. 

 The common holly is a familiar instance. In 

 this case the ribs are prolonged into stiff and 

 prickly points, which wound the tender noses 

 of donkeys or cattle. We can easily see how 

 such a protection could be acquired by the 

 holly-bush through the action of Variation and 

 Natural Selection. For holly grows chiefly in 

 rough and wild spots, where all the green leaves 

 are liable to be eaten by herbivorous animals. 

 If, therefore, any plant showed the slightest 

 tendency towards prickliness or thorniness, it 

 would be more likely to survive than its un- 

 protected neighbours. And indeed, as a matter 

 of fact, you will soon see that almost all the 

 bushes and shrubs which frequent commons, 

 such as gorse, butcher's broom, hawthorn, 

 blackthorn, and heather, are more or less spiny, 

 though in most of these cases it is the branches, 

 not the leaves, that form the defensive element. 

 Holly, however, wastes no unnecessary material 

 on defensive spikes ; for though the lower leaves, 

 within reach of the cattle and donkeys, are very 

 prickly indeed, you will find, if you look, that 

 jthe upper ones, above six or eight feet from the 

 /ground, are smooth-edged and harmless. These 

 upper leaves stand in no practical danger of 

 being eaten, and the holly therefore takes care 

 to throw away no valuable material in protecting 

 them from a wholly imaginary assailant. 



Often, too, in these prickly plants we can 

 trace some memorial of their earlier history. 

 Gorse, for example, is a peaflower^*by family, a 



