220 EXPERIMENT STATION RECORD. 



rapid lo.ss there followed a period of very slow loss of water. In addition to 

 the mechanical adjustment to prevent loss of water there is some indication of 

 an iucreasinjr acidity of the cell sap, which possibly aids materially in reducing 

 transpiration, although the present investigation does not demonstrate such a 

 relation. 



A discussion of the water lialance and its relation to desert flora is given. 



A new method for estimating the gaseous exchanges of submerged plants, 

 F. F. Blackman and A. M. Smith {Proc. Roy. .S'oc. [London'l, Scr. B, 83(1911), 

 Ao. B 565, pp. 37Ji-38S, figs. 2 ) . — A method is described for estimating the gase- 

 ous exchanges of submerged plants, which consists essentially of passing a con- 

 tinuous current of water containing dissolved carbon dioxid over the assimi- 

 lating plant and determining the difference in the carbon dioxid content of the 

 water before and after contact with the plant as a measure of the assimilation 

 taking place. 



On assimilation in submerged water plants, and its relation to the con- 

 centration of carbon dioxid and other factors, F. F. Blackman and A. M. 

 Smith (Proc. Roy. Soc. [London], Scr. B, 83 {1011), No. B 565, pp. 38d-Jfl2, 

 dgms. 9). — In a previous paper (E. S. R., 18, p. 923) it was shown that assimi- 

 lation by green leaves* was determined by the limiting factors of light, tem- 

 perature, and carbon dioxid. In the present paper an account is given of a 

 quantitative study of assimilation in submerged plants along similar lines, the 

 studies being made with several species of aquatic plants with the apparatus 

 described above. 



The nature of the relation between assimilation and the environmental char- 

 acters of carbon dioxid, light intensity, and temperature was found to be such 

 that the magnitude of assimilation In every combination of the factors was 

 determined by some one of them acting as the limiting factor. When so lim- 

 ited, an increase of that factor was found to bring about an increase in the 

 magnitude of assimilation. As an example the authors found with constant 

 light and temperature, but with increasing carbon dioxid content of the water, 

 that iihotosynthesis increased up to a certain degree, beyond which there was 

 a sudden drop unless more light or a higher temperature was employed. 



Studies on the relation of the living cells to the transpiration and sap 

 flow in Csrperus, II, J. B. Overton (Bot. Gaz., 51 (1911), No. 2, pp. 102-120, 

 figs. 2). — In a previous paper (E. S. R., 24, p. 626) an account is given of the 

 effect on transpiration of killing portions of stems with steam or hot wax, and 

 in the present paper experiments are described with various poisons, the stems 

 being killed with xylol, picric acid, alcohol, copper sulphate solution, corrosive 

 sublimate, etc. 



The experiments with the poisons show that the different kinds influence the 

 subsequent rate of evaporation of water from the plants, and that in many 

 cases the new rate far exceeds the normal transpiration of a plant of the same 

 age and superficial area. It seems certain that in the case of plants poisoned 

 throughout, the elevation of water in the stems and its evaporation from the 

 leaves in larger quantities than normally occurs in living plants depend purely 

 upon physical processes. 



Summarizing the results of the different experiments the author shows that 

 no matter how long the section killed by steam may be, the leaves never wither 

 quite so quickly as those cut and not placed in water, but kept under the sf#me 

 conditions of light, temperature, and moisture. A certain amount of water is 

 raised through the steamed portion, but it gradually diminishes until the leaves 

 become air dry. Diminution in the water supply is partially due to a blocking 

 of the vessels with a gumlike substance, which probably owes its origin to the 

 disorganization of the contents of the sieve tubes caused by heating the stems. 



