AGRICULTURAL BOTANY. 219 



Commercial fertilizers, E. Fulmer (Washington Sta. Bui. 98, pp. 24). — This 

 bulletin contains the text of the state fertilizer law, a statement regarding the 

 use of fertilizers in Washington, explanations regarding the sources, character, 

 and prices of fertilizing materials, and analyses and valuations of fertilizers 

 inspected during 1910. 



AGRICULTURAL BOTANY. 



The water balance of succulent plants, D. T. MacDougal and Effie S. 

 Spalding {Carnegie Inst. Washinylon Pub. l.'/l, pp. 77, pis. S, dgnis. 16). — Atten- 

 tion is called to the fact that many plants have a capacity for absorbing and 

 conducting water far in excess of the amount they give off, the flora of Arizona, 

 Nevada, and Sonora being especially rich in forms which carry a large water 

 balance. A series of observations covering several years has been made for the 

 purpose of determining the amount of the balance, its variations, the factors 

 influencing its volume, the relation of the various proportions of the balance 

 to growth, and the reversible changes to which such plants are subject. The 

 studies were made principally with the giant cactus {Carnegiea gtgantca), 

 bisnaga (Eehinocactus toislizeni), and some of the common prickly pears 

 (Opuntia spp. ). 



In the investigations on form alteration and growth of cacti, as shown by 

 previous studies, it was found that the giant cactus not only possesses a struc- 

 ture remarkably fitted for the storage of a large quantity of water, but also, 

 without the slightest interference with the efficiency of its mechanical system, 

 adjusts itself by a change of fqrm to the increased supply taken up from the 

 soil after a rain, and to its diminution during subsequent periods of drought. 



The observations in the present paper confirm those relating to the me- 

 chanical adjustment of the trunk of the giant cactus and show that insolation 

 is a strong secondary factor operating in conjunction with the water supply 

 and modifying its effects. Changes of air temperature were found to produce 

 slight expansion and contraction of the trunk, but in most cases the minor 

 changes were obscured bj^ those caused by variations in soil moisture. 



Discussing the growth of the giant cactus, or sahuaro, it is said that for a 

 few years growth is apical, the increments of succeeding years increasing in 

 diameter until the trunk attains the full thickness, which is afterwards main- 

 tained throughout life. The average yearly growth in height of individuals is 

 between 10 and 12 cm., and from the data collected it appears that a giant 

 cactus requires approximately 100 years to attain a height of 10 meters. 



The percentage of water in the healthy sahuaro ranges from 75 per cent of 

 the fresh weight in its lower part to more than 90 per cent in its upper part. 

 A plant 6 meters high absorbed and stored approximately 412 liters of water 

 between November, 1906, and March, 1907, in addition to the amount transpired. 

 Transpiration from the trunk is slow, but is quite rapid from flowers and flower 

 buds, the average transpiration of a fully opened flower being at least 850 mg. 

 an hour in full sunlight. 



Comparative studies with fechinocactus showed that its structural features 

 are essentially the same for mechanical adjustment as those of the giant cactus. 

 Some differences, however, are noted in mode of growth. In the Opuntia the 

 mechanical adjustment is provided in a somewhat different way, the joint 

 swelling or shrinking with the amount of wat«r received or lost. 



In discussing the water balance it is showTi that these succulent plants can 

 lose a large amount of the water contained in them without appreciable injury, 

 practically all specimens surviving for a year after the water supply had been 

 cut off. Weighings were made of a number of specimens, and after a rather 



