von Schrenk — Trees of St. Louis as Ivfluenced by Tornado. 37 



Bohra and Breitenlohner,* Becquerel,t Krutzsch,t find the 

 internal temperature of a healthy tree normally lower than 

 that of the air, but later researches have shown that, as a rule, 

 the temperature of the layers under the bark is higher by 

 several degrees than the surrounding air. Raraeaux § finds 

 that in a poplar branch, 4 cm. in diameter, the internal tem- 

 perature was 4°, 8°, and 13° C. warmer than the outside air. 

 Ihne II finds the maximum air temperature at about 3 P, M. 

 to be always below that of the tree, often many degrees, 

 Vonhausen ** measured the temperature of a large number of 

 beeches under varying conditions and computes the maximum 

 temperature on the W. S. W. side between the bark and wood 

 120° F. with an air temperature of 91°. He emphasizes the 

 fact that tender cells, like those of the cambium, cannot with- 

 stand so high a temperature for along time. Russell ft says: 

 " The temperature of the tree as a general rule ranged higher 

 than the outside." When the leaves were removed from a 

 tree of Abies balsamea the temperature between the wood 

 and bark was 4-5° higher than in an uninjured tree. Ram- 

 eaux records a similar increase in temperature in trees whose 

 branches had been removed, amounting to 8-10° C. Hartig 

 explains this increase by " the fact that the trees had small 

 crowns, and that little water found its way into the younger 

 wood rings." XX The trees in which for some reason the 

 transpiration current had been stopped or much reduced 



* Bohm u. Breitenlohner, Die Baumtemperatur in ihrer Abhangigkeit 

 von ausseren Einfliissen. Wiener Akad. Sitzber. d. math. nat. Classe 

 75:615. I. Abth. 



t Becquerel, Compt, Rendus etc. 47: 717. 1858; 48: 764. 1859. 



X Krutzsch, H. Untersuchungen liber die Temperatur der BJiume etc. 

 Kon. Siich. Akad. f. Forst u. Landwirte zu Tharand 10. 1854. 



§ Rameaux, M. Des temperatures veg^tales. Ann. d. Sci. nat., Bot. 

 19:1. 1843. 



II Ihne, Egan. Uber Baumtemperatur unter der Einfluss der Insola- 

 tion. Allg. Forst u. Jagdzeit. (Supplement) 12. Heft 4. 



** Vonhausen, W. Untersuchung iiber den Rindenbrand der Biiume. 

 Allgem. Forst u Jagdzeit. 49: 8. 1873. 



tt Russell, H. L. Observations on the temperature of trees. Bot. Gazette 

 14:216. 1889.— See also Hess, iJber den Rindenbrand. Forstschutz 541- 

 49. 1878. 



XX Hartig, R. Diseases of Trees (tr. by Somerville & Ward) 295. 1894, 



