148 Physiologie. 



in weight of 20 gms, which are added to the scale pan, special Pro- 

 vision being made to prevent two balls from being delivered in rapid 

 succession; no record is made unless the ball is actually delivered 

 to the ball Container or beam. A spring motor is provided to litt 

 the beam when a ball is delivered, a necessary feature when the 

 plants are exposed to wind. Records of the time at which each ball 

 is delivered are made upon a modification of the recorder devised 

 by M arvin for use in connection with automatic rain gages. To 

 illustrate the kinds of records obtained, several representative graphs 

 of transpiration, constructed from records made by this Instrument, 

 are presented, although the complete results of the work with this 

 Scale are reserved for a future paper. Earlier forms of transpira- 

 tion balances are briefly described, and illustrated. The instruments 

 are divided into two classes: 1) The step-by-step type, which in- 

 cludes the new form described, in which small weights of equal 

 value are added to the scale pan in succession, or in which a 

 counterpoise is advanced in equal Steps; 2) the continuous record 

 type, in which the plant is suspended from a spring, or from a 

 variable lever, or is mounted on a float. Sam F. Trelease. 



Gortner, R. A. and J. A. Harris. Notes on the technique 

 ofthe determination ofthe depression ofthefreezing 

 point of vegetable saps. (Plant World. XVII. p. 49—53. 1914.) 



Samples of tissues are placed in test tubes, which are sealed, 

 and plunged iramediatel}^ into a freezing mixture of salt and ice. 

 Freezing serves to preserve the tissues and render them permeable. 

 The frozen tissues are thawed, and the sap extracted b}^ means of 

 a heavily tinned press. Suspended particles are then removed from 

 the sap, preferably by centrifuging. The Beckmann method of 

 determining osmotic pressure by freezing point lowering is modified 

 for rapidity and accuracy of manipulation. Sam F. Trelease. 



Hooker, H. D. Jr., Thermotropism in roots. (Plant World. 

 XVII. p. 135—153. 1914.) 



This paper describes a series of experiments upon the bending 

 of roots when subjected to a one-sided heat Stimulus. The account 

 is prefaced by a historical review of earlier work bringing out the 

 conflicting nature of the conclusions hitherto reached and sbowing 

 the need for further experimentation. The roots of seedlings gro- 

 wing in moist sawdust contained in a zinc box heated on one side 

 and cooled on the other were found to bend toward the cooler 

 side, suggesting that the bending was hydrotropic rather than 

 thermotropic and depended upon the moisture conditions of the 

 sawdust. To avoid moisture effects, the seedlings were grown in 

 small boxes of agar jelly and under the circumstances the establish- 

 ment of a temperature gradient through the agar was never followed 

 by a bending away from the higher temperature. Since the moisture 

 conditions in the agar are the same on all sides of the root, the 

 author concludes that roots do not respond to a one-sided heat Sti- 

 mulus by bending, and that the so called „thermotropic" reactions 

 are really due to hydrotropism, perhaps parlly to traumatropism 

 in the case of higher temperatures. F. M. Hildebrandt. 



