1916] AGRICTJLTURAL BOTANT. 733 



in the day at lower elevations and later at higher ones. The values for the 

 transpiring power in all eases were found to be higher at the lower elevations, 

 but at the higher elevations the values are sustained through a longer portion 

 of the day. 



The interrelation of transpiration, root absorption and water-absorbing 

 capacity of tissues in an Opuntia, Euith B. Shee\^ (Abs. in Science, n. ser., 43 

 (1916), No. 1106, pp. 361, 362). — The author gives a summary of investigations 

 conducted to test the conclusion of other workers that the transpiring power 

 is greater in cacti during the night than during the day. 



As a result of her investigation it was found that the transpiring power is 

 greatly influenced by light intensity, air temperature, water content of tissues, 

 and available soil water. The day to night variations in transpiring power of 

 tissue are independent of any day to night variations in root absorption. 

 During the daylight hours more water was absorbed by the root than was 

 lost by transpiration, while at night the reverse was true. Variations in water 

 intake by the roots are due, on the one hand, to variations in the soil reten- 

 tivity, and, on the other, to variations in the plant itself. Stomata, as a rule, 

 are shut during the day and open at night, but it was not possible to ascertain 

 whether the closing of the stomata accompanies or follows a decrease in trans- 

 piration rate. The water-absorbing power of pieces cut from internal tissue 

 was less during the night than during the day, being least from 4 to 5 a. m. 

 and greatest from 3 to 5 p. m. This was true whether the calculations were 

 based on dry weight or on the original weight of the material. The author 

 advances the theory that the water-absorbing capacity of the internal tissue 

 controls the secondary absorbing power of the roots, and probably also the 

 transpiring power. 



The influence exerted by light intensity and air temperature, together with 

 their duration, show that the variations in absorbing capacity are due, at 

 least in part, to chemical changes brought about by the metabolic processes, 

 and many tests show that the changes in the water-absorbing capacity of the 

 tissues parallel acidity changes in the plants in such a way that when acidity 

 is highest the absorbing capacity is lowest, and vice versa. Certain exceptions 

 occur, however, which show that the relation can not be so simple as the 

 influence of mere changes in hydrogen ion concentration. Other factors, it is 

 claimed, must be taken into consideration, including the accumulation and 

 disappearance of the salts of organic acids. The author claims that it is 

 impossible to state as yet whether the absorbing capacity of the internal tissue 

 is due to colloidal absorption, osmotic forces, or both. 



Measurement of the surface forces in soils, C. A. Shxjll (Ahs. in Science, 

 n. ser., 4S (1916) , No. 1106, p. 361 ) . — An examination of the absorption of water 

 by dry Xanthium seeds is said to have shown that the internal forces had an 

 initial value of at least 965 atmospheres. The internal forces have been deter- 

 mined at various moisture contents. Dry seeds were used to measure the 

 surface holding power of soils for water, with the result that both the seeds 

 and air dry soil were found to have approximately the same force. 



As the capillary moisture increased, the surface moisture decreased until, 

 at the wilting coefiicient of the soil, the amount of back pull exerted was not 

 more than 3 or 4 atmospheres. This relation was found to hold essentially 

 for all types of soils from heavy clay to sand. The soil, at the critical moisture 

 content of the plant, it is claimed, holds the water with less force than the 

 osmotic pressure of the root hairs of the plant, as determined by plasmolytic 

 methods. The wilting of the plant, it is believed, does not result from lack 

 of moisture or lack of a gradient toward the plant, but probably from the low 

 rate of movement of water due to the friction in thin films. 



