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SCIENCE 



[N. S. Vol. XXXVIII. No. 971 



to be erroneous by calling attention to tbe 

 facts that ice contracts as the temperature 

 sinks while clefts in tree trunks open farther 

 and farther as the temperature drops, i. e., 

 were the opening of the clefts due to the for- 

 mation of ice they would close again as the 

 temperature sank lower. As a matter of fact 

 tree trunks begin contracting above the freez- 

 ing point of water, as may be gathered from 

 Caspary's records given in the above cited 

 papers on the opening and closing of clefts, as 

 well as from direct measurement of circum- 

 ferences." 



According to the figures in text-books of 

 physics changes in the lengthwise dimension 

 of wood due to a change of temperature are 

 only slight as compared to changes resulting 

 in transverse direction. The transverse con- 

 traction of wood is given as nearly the same as 

 the linear contraction of ice. It has been sug- 

 gested that different types of tree tissues eon- 

 tract at different rates and that the branches 

 of trees are caused to move up and down by 

 changes of temperature owing to a differential 

 contraction and expansion of the tissues on 

 the two sides. 



The literature of branch movements of trees 

 is rather meager and not generally known, as 

 may be gathered from an article which ap- 

 peared in 1904, entitled, " An TJndescribed 

 Thermometric Movement of the Branches in 

 Shrubs and Trees,'" as well as from some 

 recent correspondence with C. C. Trowbridge 

 who has made a study of the subject but had 

 found only Ganong's paper. The earliest pub- 

 lished observations and experiments found on 

 branch movements induced by changes in tem- 

 perature were by Geleznow." He noted that 

 branches of certain trees sink during cold 

 weather and rise again as it becomes warmer. 



'"Crown-rot of Fruit Trees: Field Studies," 

 N. Y. State Agri. Expt. Sta. Technical Bull., 23: 

 35-39, 1912. 



* W. F. Ganong, Ann. Bot., 18 : 631-44, 1904. 



' N. Geleznow, ' ' Eecherches sur la quantity et la 

 repartition de I'eau dans la tige des plantes lig- 

 neuses," Melanges Biol. Acad. Imper. Se. St. 

 Petersb., 9: 667-85, 1877. 



During a thaw branches of linden, birch, elm, 

 and other epinastic species were cut and fixed 

 in horizontal position by their bases, some with 

 their lower sides uppermost; and the position 

 of the tips was marked. As the temperature 

 became lower the inverted branches moved in 

 a direction opposite to that of the branches in 

 normal position, indicating that the direction 

 of movement depends on the make-up of the 

 branches. It was noted, however, that al- 

 though pine branches are hyponastic and 

 linden branches epinastic, both bend dovsm- 

 ward as the temperature sinks, showing that 

 the nature of the eccentricity could not be 

 the cause of these movements. 



The relative amounts of water contained in 

 the wood of the lower and upper sides of 

 branches gave no convincing results, although 

 it seemed possible that this might have a 

 causal relation to the movement. It was 

 found that the wood on the upper side of pine 

 branches had a greater water content than that 

 on the lower, while in the case of birch and a 

 number of other trees the wood on the under- 

 side contained more water than that on the 

 upper. The water determinations were made 

 once each month throughout the year and are 

 interesting aside from any bearing they may 

 have on branch movements. For instance, the 

 bark on the larch was found to contain more 

 water throughout the year than the wood; the 

 wood often contains less water toward the dis- 

 tal end of branches, while the bark usually 

 contains more. 



Caspary also made some very interesting 

 observations the year following the studies by 

 Geleznow," although the work was not pub- 

 lished until much later. The positions of the 

 ends of convenient branches of ten species of 

 trees were marked on upright stakes driven in 

 the ground and their locations redetermined 

 about sun-up each day from November 29, 

 1865, to March 24, 1866. Heavy dew and rain 

 were found to cause a slight depression of 

 branches and snow induced considerable sink- 



° B. Caspary, ' ' Uber die Veranderungen der 

 Eiehtung der Aste holziger Gewiiehse bewirkt 

 duTch niedrige Warmegrade, " Internat. Hort. Ex- 

 hibit Bot. Congress, London, 3: 98-117, 1886. 



