546 Forestry Quarterly 



acter of the seedlings that if left undisturbed the forest in most 

 cases would slowly, but surely, change again to approximately 

 the climax type. C. D. H. 



Torreya, Vol. 13, Nos. 5 and 9; Vol. 14, No. 10. Bulletin Torrey Botanical 

 Club, Vol. 42. 



BOTANY AND ZOOLOGY 



An investigation was carried on during 

 Winter two winter seasons at the University of 



Temperature Michigan by Ehlers to determine the efTect 



of of solar radiation upon the internal temper- 



Pine Leaves ature of persistent leaves and its possible 



bearing upon photosynthesis and the accu- 

 mulation of reserve food material under winter conditions. It 

 has been known for some time that apparently the reserve carbo- 

 hydrates in deciduous trees reached their maximum at leaf-fall, 

 decreased a little in the winter and reached their minimum with 

 the formation of new shoots in the spring. The condition of 

 stored materials is practically reversed in the case of the ever- 

 green trees. Instead of the maximum appearing in the autumn, 

 there is a constant increase of reserve material during the winter 

 and a maximum is reached only at the beginning of spring. If 

 this is true, it would seem that trees with persistent leaves con- 

 tinue to manufacture food during the low temperature "rest- 

 period" of the winter months. 



Now just what is the internal temperature of the leaves when 

 this winter food manufacturing is taking place? This is the 

 question the present investigator attempted to answer. By means 

 of a slide wire wheatstone bridge, galvanometer, voltmeter 

 thermo-junctions, and necessary accessories, with a lead wire 

 piercing two leaves at an angle of 45 degrees with their long 

 axis, he was able to record the differences between internal and 

 external temperatures of the leaves at various times and under 

 various conditions of atmosphere. The apparatus was placed 

 upon a high platform to bring it up among the leaves of an 

 Austrian pine tree, and it was connected up with the ground 

 floor of the adjacent physics laboratory where the measuring 

 apparatus was kept. The investigator found that i\\t leaves 



