1917] AGRICULTURAL BOTANY. 823 



able the liquid pressure generated by a chemical reaction (respiration) which 

 produces water at the expense of a gas, or by a physical change of state, pro- 

 ducing water by the condensation of vapor. This latter mechanism, according 

 to the theory here proposed, is responsible for root pressure. The condensation 

 involves a direct conversion of energy, 90 per cent of the latent heat of vapor 

 being theoretically convertible into liquid pressure. The ultimate source of 

 energy Is the combined action of capillary imbibition and solar heat on soil 

 particles of different sizes, which produces a slight supersaturation in the 

 soil interstices. 



The second function of the root, the absorption of nutrient salts. Is supposedly 

 effected by alternate extrusion and absorption through the root hairs of an 

 acidic solvent. It is further suggested that in plant circulation, the whole 

 upward current is in the xylem and the downward movement in the phloem, 

 the medullary rays maintaining the continuity at all levels. 



The cryoscopic constants of expressed vegetable saps as related to local 

 environmental conditions in the Arizona deserts, J. A. Harris, J. V. Law- 

 rence, and R. A. Gortner (Physiol. Researches, 2 (,1916), No. 1, pp. 49). — The 

 results of the studies here outlined are considered to show that concentration 

 of the cell sap, in the plants characteristic of different habitats, shows a certain 

 differentiation. The average values obtained are lowest for the arroyo or 

 sandy wash, then successively higher for the canyons and foothills, the sandy 

 slopes, the bajadas or mesalike slopes, and finally the salt spots. For the 

 region as a whole, within working distance of Tucson, Ariz., the cryoscopic de- 

 terminations show concentrations for trees and shrubs of 28.1, dwai-f and 

 half-shrubs 21.45, perennial herbs 16.35, and winter annuals 14.73 atmospheres. 

 ' Depression of the freezing point in triturated plant tissues and the mag- 

 nitude of this depression as related to soil moisture, R. P. Hibbard and O. E. 

 Harrington (Physiol. Researches, 1 (1916), No. 10, pp. 441-454). — The work 

 here outlined, employing material from potato tubers, cabbage head leaves, 

 apples, lemons, oranges, grapefruits, onion bulbs, and maize roots and tops, 

 is considered to show that the lowering of the freezing point in ground plant 

 tissues is as valuable a criterion for the comparison of osmotic concentrations 

 in the tissues as is the corresponding index for the expressed sap. The material, 

 after being frozen, then triturated, and finally tested in a Beckmann freezing- 

 point apparatus, gave concordant results from different samples of the same 

 pulp and from pulps as compared with juices expressed from samples of the 

 same pulp, provided the pressing had been thorough. Thus the determination 

 of the freezing-point depression and of the osmotic concentration of tissues Is 

 rendered more simple, though the method is admittedly inapplicable to very 

 small quantities of materials. 



By this method, material from maize roots showed a much lower osmotic con- 

 centration than did material from the aerial portions. 



Studies of protoplasmic permeability by measurement of rate of shrinkage 

 of turgid tissues. — I, The influence of temperature on the permeability of 

 protoplasm to water, B. M. Delf (Arm. Bot. [London], SO (1916), No. 118, pp. 

 28S-S10, figs. 17; abs. in Rpt. Brit. Assoc. Adv. Sci., 85 (1915), pp. 128-125, 

 fig. 1). — Developing a method of measuring Indirectly changes in the perme- 

 ability of protoplasm to water by ascertaining the changes in the rate of shrink- 

 age of tissue bathed in solutions tending to plasmolyze the cells, the author 

 studied the changes In protoplasmic permeability corresponding to temperature 

 changes between 5 and 42° C. In discussing the tissue shrinkage obtained in 

 dilute sugar solution, he states that the permeability of protoplasm for water 

 is increased by increase in temperature so far as studied (up to about 42°), 

 98133°— No. 9—17 3 



