Vol. 32 



BULLETIN 



No. 2 



OF THE 



TORREY BOTANICAL CLUB 



FEBRUARY, 1905 



Mechanical adjustment of the suaharo (Cereus giganteus) to varying , 



quantities of stored water 



Effie Southworth Spalding 

 (With plates 3 and 4) 



Among the desert plants of the southwestern United States 

 that are provided with a w^ell-developed system for water-storage, 

 certain cacti, particularly those of columnar form, are conspicuously 

 fluted with strong ribs and corresponding furrows that extend 

 from base to apex of the stem. This structure naturally suggests 

 a ready adjustment of the plant, by a bellows-like action of its 

 ribs and furrows, to changes in bulk due to varying amounts of 



r 



stored water. It is obvious, however, that such an adjustment, if 

 it satisfies the requirements of successful adaptation, must not 

 impair the efficiency of the general mechanical system ; since 

 these plants, rising like a columnar water-tank, often to the height 

 of 50 or 60 feet, from a narrow base, are subjected to the force of 

 high winds from evGry point of the compass. 



To ascertain whether this bellows-like action actually takes 

 place, a series of measurements and observations were undertakers 

 at the Desert Laboratory during the winter of 1903-4. These 

 were begun by the resident investigator, Dr. W. A. Cannon, and, 

 at his suggestion, were afterwards carried out and extended by 

 myself. 



An inspection of a cross-section of the stem of a giant cactus 

 will show a heavy band of thick- walled subepidermal tissue, w^hich 

 is exceedingly strong and elastic. Beneath this is a band of thin- 

 walled chlorophyl-cells, and all the tissue between this and the 



[The Bulletin for January (32 : I-S5,//. A ^) was issued 23 F 1905. j 



57 



