A DESERT FRUIT. 65 



and palates, but which supply them at. least with a little 

 food and moisture : so the plants are compelled in turn 

 to take almost extravagant precautions. Sometimes the 

 leaves end in a stout dagger-like point, as with the agave, 

 or so-called American aloe ; sometimes they are reduced 

 to mere prickles or bundles of needle-like spikes ; some- 

 times they are suppressed altogether, and the work of 

 defence is undertaken in their stead by irritating hairs 

 intermixed with caltrops of spines pointing outward from 

 a common centre in every direction. When one remem- 

 bers how delicately sensitive are the tender noses of most 

 browsing herbivores, one can realize what an excellent 

 mode of defence these irritating hairs must naturally con- 

 stitute. I have seen cows in Jamaica almost maddened 

 by their stings, and even savage bulls will think twice in 

 their rage before they attempt to make their way through 

 the serried spears of a dense cactus hedge. To put it 

 briefly, plants have survived under very arid or sandy 

 conditions precisely in proportion as they displayed this 

 tendency towards the production of thorns, spines, 

 bristles, and prickles. 



It is a marked characteristic of the cactus tribe to be 

 very tenacious of life, and when hacked to pieces, to 

 spring afresh in full vigour from every scrap or fragment. 

 True vegetable hydras, when you cut down one, ten 

 spring in its place : every separate morsel of the thick 

 and succulent stem has the power of growing anew into 

 a separate cactus. Surprising as this peculiarity seems 

 at first sight, it is only a special desert modification of a 

 faculty possessed in a less degree by almost all plants 

 and by many animals. If you cut off the end of a rose 



F 



