Current Literature 483 



gas and yet sufficient channels remain for the transpiration stream 

 to supply the needed water for evaporation from the leaves. 

 Only when the gas bubbles extended continuously in a horizontal 

 plane across the entire diameter of the stem could they make his 

 theory inoperative. This condition undoubtedly never occurs in 

 a living tree. 



When dealing with living organisms, it is, in the opinion of the 

 reviewer, practically impossible to select a definite factor and say 

 that it is the cause of a given phenomenon. It is probable, 

 therefore, that several forces, such as osmotic pressure in the living 

 wood elements, and surface tensions in the dead wood elements, 

 contribute a portion of their energies to the rise of water in trees. 

 It is probable also that some of the forces are more effective than 

 others, and in reading the book under review one can hardly help 

 being convinced by Dixon's masterly presentation of his theory. 



C. D. H. 



The Killing of Plant Tissues by Low Temperature. By W. H. 

 Chandler. Research Btdletin 8, University of Missouri. Co- 

 lumbia, Mo. 1913. Pp. 143-309. 



While the subject matter of the above bulletin is chiefly con- 

 cerned with the conditions of freezing of fruit trees, yet it contains 

 considerable data of general application in regard to the phenome- 

 non of freezing. The resiilts of many investigations have shown 

 that during freezing (which may or may not result in freezing to 

 death), ice forms in the tissue, generally not in the cells, but in the 

 intercellular spaces, the water moving out of the cells to form 

 crystals in these spaces. The most commonly accepted theory is 

 hat killing from cold results from the withdrawal of water from 

 the protoplasm. The amount of water loss necessary to result in 

 death varies with different plants and different tissues. Some 

 interesting variations of this theory have recently been developed. 

 For example, one investigator found that when plant sap is frozen, 

 certain proteids may be precipitated out and apparently those 

 plants most easily killed by freezing have their proteids precipi- 

 tated out at the highest temperature. Thus begonia, which is 

 very easily killed, had its proteids precipitated out at — 3° C, 

 while the sap of pine needles, not easily frozen, required a tem- 

 perature of — 40° C. to precipitate any proteids. He accounts 



