Band 140. Nr. 1. XL. Jahrgang. I. Bd. Nr. 1. 



Botanisclies Centralblatt 



Referierendes Organ 



der 



Association Internationale des Botanistes 

 für das Gesamtgebiet der Botanik. 



Herausgegeben unter der Leitung 

 des Präsidenten: des Vice- Präsidenten: des Secretärs: 



Dr. D. H. Scott. Prof. Dr. Wm. Trelease. Dr. J. P. Lotsy. 



und der Redactions-Comtnissions- Mitglieder: 



Prof. Dr. Wm. Trelease, Dr. C. Bonaventura, A. D. Gotton, 



Prof. Dr. C. Wehmer und Mag. C. Chrlstensen. 



von zahlreichen Specialredacteuren in den verschiedenen Ländern. 



Dr. J. P. Lotsy, Chefredacteur. 



No. 1. 



Abonnement für das halbe Jahr ^ Mark 

 durch alle Buchhandlungen und Postanstalten. 



1919. 



Alle für die Redaction bestimmten Sendungen sind zu richten an: 

 Redaction des Botanischen Centralblattes, Haarlem (Holland), Spaarne 17. 



Trowbridge, C. C, The thermometric movements oftree 

 branches at freezing temperatures. (Bull. Torrey. Bot. Club. 

 LXIII. p. 29—56. 19 Textfig. 1916.) 



In this investigation Ihe mechanics of the thermometric move- 

 inents of branches has not yet been determined, but the observa- 

 tions described have made an advance in the study of the subject. 

 Some of the facts which have been determined are summarized 

 below; temperatures are given in Fahrenheit. 



The measurements on the movements of large branches of Tilia 

 europaea seem to show that below 32° the movements are thermo- 

 metric; when the temperature of the air falls below 32° (or very 

 shortly above that point) the depression begins and continues until 

 at least 0°, the lowest point at which observations were made. There 

 is scarcely any movement above 32°. The freezing action of water 

 is therefore the origin of the process of depression. There seems, 

 however, to be a very slight thermometric movement just above 32°. 



By making hourly observations not made hitherto, it has been 

 shown that there raay be a lag of one or two hours in the 

 movement of the branches behind the changes of temperature, but 

 if the air temperature is changing, a very slight change in the rate 

 causes an almost immediate modification in the rate of movement 

 of the branch. The observations made thusfar indicate that a con- 

 stant State of temperature for a considerable time, slightly below 32° 

 causes a small movement; then the branch remains stationary until 

 the temperature changes. These facts lead to the conclusion that 

 the freezing liquid bringing about the thermometric movements of 

 the branches below freezing temperatures is not pure water, but a 

 Solution, namely, the sap. 



BotajQ. Centralblatt. Band 140. 1919. 1 



