642 EXPERIMENT STATION RECORD. 



the changes in temperature of the air and of limbs under various con- 

 ditions. 



When the trunks and limbs of trees are shaded their temperatures, 

 if above the freezing point of water, vary according to the temperature 

 of the outside air, but show somewhat smaller diurnal variations and 

 change more slowly, so that in shade tree temperatures above 0° C. 

 are higher than the air temperature when both temperatures are falling 

 and lower when both are rising. On the other hand, when exposed to 

 strong sunlight, again provided their temperatures are above the freez- 

 ing point of water, limbs and trunks of trees exhibit much greater 

 diurnal variations of temperature, much greater maximum daily tem- 

 peratures, and quicker changes in temperature than shaded limbs, and 

 even than the outside air, so that in strong sunlight tree temperatures 

 above 0° C. are higher than the air temperature, not only when both 

 temperatures are falling, but are often higher also when both are rising. 

 One side of even a small limb may therefore have a temperature much 

 higher than the air and the opposite side at the same time a tempera- 

 ture lower than the air. The temperatures of the center of limbs change 

 more slowly than those of the surfaces and the extreme daily variations 

 of temperature are less. Above the freezing point of water, the tem- 

 peratures of water-soaked dead limbs behave like those of live limbs, 

 while the temperatures of normal dead limbs change more quickly than 

 those of live limbs and the extreme daily variations of temperature are 

 greater. The temperatures of normal dead limbs, like the temperature 

 of the air. in both rising and falling, pass the freezing point of water 

 without appreciable retardation. The temperatures of water-soaked 

 dead limbs, in both rising and falling, are noticeably retarded at or near 

 the freezing point of water, but having once passed this point proceed 

 rapidly again. The temperatures of live limbs, in rising, behave like 

 those of water-soaked dead limbs; in falling, however, they are not 

 only retarded at the freezing point of water, but even after having 

 passed this point their descent continues slow. 



An observation on annual rings, F. W. Card (Proc. Nebraska 

 Acad. Sci., 6, 1896, pp. 243,241). — The author conducted an experiment 

 to ascertain the relation between growth rings and annual rings in 

 trees. A piece of bark was removed early in the season from the north 

 side of an ash tree and also from a maple. Later in the season both 

 trees were stripped of the leaves, which were renewed within 3 weeks. 

 In November both trees were cut down and a cross section made where 

 the bark had been removed, and the ring of growth for that year was 

 apparently as uniform as for others. It seems probable that a greater 

 interference with normal conditions of growth than that in the experi- 

 ment is necessary to produce more than one growth ring in a season. 



Osier culture, J. M. Simpson ( TJ. 8. Dept. Agr., Division of For- 

 estry Bui. 19, pp. 27). — The author gives a historical sketch of the cul- 

 tivation and use of osiers, together with notes on their geographic 

 distribution and characteristics. The subject of varieties is treated at 



