A DESERT FRUIT. 113 



indeed to the reflective mind when you've stung yourself badly 

 with them. 



The reason for this bellicose disposition on the part of the cac- 

 tuses is a tolerably easy one to guess. Fodder is rare in the desert. 

 The starving herbivores that find themselves from time to time 

 belated on the confines of such thirsty regions would seize with 

 avidity upon any succulent plant which offered them food and 

 drink at once in their last extremity. Fancy the joy with which 

 a lost caravan, dying of hunger and thirst in the byways of Sa- 

 hara, would hail a great bed of melons, cucumbers, and lettuces ! 

 Needless to say, however, under such circumstances melon, cucum- 

 ber, and lettuce would soon be exterminated ; they would be 

 promptly eaten up at discretion without leaving a descendant to 

 represent them in the second generation. In the ceaseless war 

 between herbivore and plant, which is waged every day and all 

 day long the whole world over with far greater persistence than 

 the war between carnivore and prey, only those species of plant 

 can survive in such exposed situations which happen to develop 

 spines, thorns, or prickles as a means of defense against the mouths 

 of hungry and desperate assailants. 



Nor is this so difficult a bit of evolution as it looks at first sight. 

 Almost all plants are more or less covered with hairs, and it needs 

 but a slight thickening at the base, a slight woody deposit at the 

 point, to turn them forthwith into the stout prickles of the rose 

 or the bramble. Most leaves are more or less pointed at the end 

 or at the summits of the lobes ; and it needs but a slight intensi- 

 fication of this pointed tendency to produce forthwith the sharp 

 defensive foliage of gorse, thistles, and holly. Often one can see 

 all the intermediate stages still surviving under one's very eyes. 

 The thistles themselves, for example, vary from soft and unarmed 

 species which haunt out-of-the-way spots beyond the reach of 

 browsing herbivores, to such trebly-mailed types as that enemy 

 of the agricultural interest, the creeping thistle, in which the 

 leaves continue themselves as prickly wings down every side of 

 the stem, so that the whole plant is amply clad from head to foot 

 in a defensive coat of fierce and bristling spear-heads. There is 

 a common little English meadow weed, the rest-harrow, which in 

 rich and uncropped fields produces no defensive armor of any 

 sort ; but on the much-browsed-over suburban commons and in 

 similar exposed spots, where only gorse and blackthorn stand a 

 chance for their lives against the cows and donkeys, it has devel- 

 oped a protected variety in which some of the branches grow 

 abortive, and end abruptly in stout spines like a hawthorn's. 

 Only those rest-harrows have there survived in the sharp strug- 

 gle for existence which happened most to baffle their relentless 

 pursuers. 



VOL. XII. 11 



