2OO Plant Life and Evolution 



giant cactus, or Suwarro (Cereus gigantens}, hav- 

 ing almost tree-like proportions, and showing a max- 

 imum reduction of the evaporation surface, and 

 extraordinary capacity for water storage. The ex- 

 tensively branched roots run close to the surface of 

 the ground, where they quickly absorb the rain and 

 convey it to the great pillar-shaped stem, where it 

 is stored away deep in the sappy tissues of the pith. 



The century plant (Agave), unlike the cacti, has 

 its leaves highly developed, but these are very thick 

 and fleshy, and protected by an impervious covering 

 so that they are quite as efficient water-storage or- 

 gans as the fleshy, leafless stems of the cacti. 



Another remarkable plant (Fouquiera) of this 

 same region is familiar to every observant traveler 

 through Southern Arizona. This curious shrub, 

 known locally as " Fish-pole Cactus," or " Oco- 

 tilla," is a bush consisting of a bundle of slender 

 stems, sometimes tipped with a cluster of scarlet 

 flowers, nearly or quite unbranched, and usually 

 quite bare of leaves. Periodically, however, at the 

 seasons when the brief showers of midsummer or 

 midwinter fall, the bare stems clothe themselves 

 with delicate little leaves, quite out of keeping with 

 the desert environment, and these quickly wither 

 with the cessation of the rains. 



Sometimes the leaf becomes reduced so that the 

 normal blade disappears, and a flattened leaf stalk 

 takes its place. These " phyllodia " are especially 

 perfect in some of the Australian acacias, often 



