534 BOTANICAL GAZETTE [December 



pioneers being Calamovilfa longifolia, Psoralen lanceolata, and Redfieldia flex- 

 uosa. After a time these pioneers are followed by the bunch-brass association; 

 after this vegetational changes are much less rapid. One of the chief features 

 of interest in the woodland formations along the streams is the overlap of the 

 deciduous eastern forest and the yellow pine (Pinus ponderosa scopulorum) 

 forest of the west. The lowland formations are much like those elsewhere 

 both as to content and succession, except that a meadow type represents the 

 temporary climax; probably one of the more eastern of the prairie-grass asso- 

 ciations represents a more ultimate condition. — H. C. Cowles. 



The water-balance of desert succulents. — The Sonoran desert is very rich 

 in succulents which carry a large water-balance. Some of the most striking 

 of these have been studied in detail for some years at the Desert Laboratory. 7 

 Mrs. Spalding had previously shown that the stems of Cereus giganteus 

 expand and contract in a most remarkable manner, as water is accumulated 

 or lost. 8 These movements are readily measured by noting the variations in 

 distance between the ridges from time to time. Mrs. Spalding, as her part 

 of the contribution, reports greatly extended experiments along this line on the 

 same and on additional species. The earlier work has been confirmed in prac- 

 tically all respects. In addition to the influence of soil water in changing the 

 plant form, insolation is found to be an important secondary factor; for 

 example, the furrows on the south sides of stems are narrower than those on the 

 north sides. The behavior of Echinocactus Wislizeni is much like that of 

 Cereus giganteus, but in Opuntia the behavior is simpler, consisting merely of 

 the swelling and shrinking of the stem segments. 



MacDougal's part of the work consisted of a study of variations in the 

 water-balance, due to seasonal moisture fluctuations and other causes. The 

 remarkable ability of these desert succulents to tide over long periods of drought 

 is brought out in striking fashion in the case of plants of Cereus giganteus, in 

 which branches have remained alive and even have bloomed a year after the 

 main trunk bearing them has died. More efficient even than the cacti is 

 Ibervillea sonorae, a plant whose stem base is tuberized. For ten years tubers 

 of this species have remained alive, without a renewal of water supply, sending 

 up short green stems each summer; during this time but half of the original 

 weight had been lost. In the general conclusions attention is called to great 

 differences in individual behavior under similar experimental conditions. The 



7MacDougal, D. T., and Spalding, E. S., The water-balance of succulent 

 plants. Carnegie Institution of Washington, Publication 141. pp. 77. pis. 8. i9 10 - 

 See also MacDougal, D. T., The water-balance of desert plants. Ann. Botany 

 26:71-93. pis. 5. 1912. 



8 Spalding, E. S., Mechanical adjustment of the Sahuaro (Cereus giganteus) to 

 varying amounts of stored water. Bull. Torr. Bot. Club 32:57-68. 1905; see Bot. 

 Gaz. 40:396. 1905. 



