n 4 THE POPULAR SCIENCE MONTHLY. 



Desert plants naturally carry this tendency to its highest 

 point of development. Nowhere else is the struggle for life so 

 fierce ; nowhere else is the enemy so goaded by hunger and thirst 

 to desperate measures. It is a place for internecine warfare. 

 Hence, all desert plants are quite absurdly prickly. The starving 

 herbivores will attack and devour under such circumstances even 

 thorny weeds, which tear or sting their tender tongues and pal- 

 ates, but which supply them at least with a little food and moist- 

 ure : 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 ; 

 sometimes they are suppressed altogether, and the work of defense 

 is undertaken in their stead by irritating hairs intermixed with 

 caltrops of spines pointing outward from a common center in 

 every direction. When one remembers how delicately sensitive 

 are the tender noses of most browsing herbivores, one can realize 

 what an excellent mode of defense these irritating hairs must 

 naturally constitute. I have seen cows in Jamaica almost mad- 

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

 their rage before they attempt to make their way through the ser- 

 ried spears of a dense cactus hedge. To put it briefly, plants have 

 survived under very arid or sandy conditions precisely in propor- 

 tion as they displayed this tendency toward 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 vigor 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 ani- 

 mals. If you cut off the end of a rose branch and stick it in the 

 ground under suitable conditions, it grows into a rose tree. If 

 you take cuttings of scarlet geraniums or common verbenas, and 

 pot them in moist soil, they bud out apace into new plants like 

 their parents. Certain special types can even be propagated from 

 fragments of the leaf ; for example, there is a particularly viva- 

 cious begonia off which you may snap a corner of one blade, and 

 hang it up by a string from a peg or the ceiling, when, hi presto ! 

 little begonia plants begin to bud out incontinently on every side 

 from its edges. A certain German professor went even further 

 than that: he chopped up a liverwort very fine into vegetable 

 mincemeat, which he then spread thin over a saucerful of moist 

 sand, and lo ! in a few days the whole surface of the mess was cov- 



