A DESERT ERUJT. f)!^ 



arrangod geometrically ^Yitll great regukuity in a perfect 

 quiucunx. But that is a small consolation indeed to the 

 reflective mind when you've stung yourself badly with 

 them. 



The reason for this bellicose disposition on the part of 

 the cactuses 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 whi'ch oliered 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 Sahara, would hail a great bed of melons, cucumbers, 

 and lettuces ! Needless to say, however, under such cir- 

 cumstances melon, cucumber, and lettuce would soon be 

 exterminated : they would be promptly eaten up at dis- 

 cretion without leaving a descendant to represent them 

 iu the second generation. In the ceaseless war between 

 herbivore and plant, which is waged every day and all 

 clay 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 defence 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 shght 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 



