1 



ECOLOGICAL CROSS SECTION OF THE MISSISSIPPI. 



133 



The main point to be remembered in judging temperature 

 conditions in the field from data obtained in the city is that 

 true extremes are seldom obtained in the latter location on 

 account of the lesser radiation of brick structures. Both in 

 winter and summer, during the day as well as at night, the 

 extremes of tempera 

 field. This is larcch 



ure are less in the cities than in the 

 due to the lack of protection from wind 



of 



be observed 

 itory having 



as to be negligible, 



a different nature, 

 shown a variation 



same hour and on 



Measurements at various stations have 

 f from 2 to lO'^ C. at approximately the 

 le same date. In summer the temper- 

 is is at least 4^ C. lower than that of the 



field, while at night it is as much higher. 



figu 



on a limited number of observations made near Jefferson 

 Barracks during 1907. The need of automatic instru- 

 ments for the registration of temperatures, etc., is, how- 

 ever, indicated. This, in the vicinity of a large city, ap- 

 pears to be hopeless, even the most simple and seemingly 

 well-hidden instruments being subject to vandalism. 



In a former paper* attention was called to the protective 



action of forests, 

 moisture, as sho\^ 



temperature and 



t Comparative ob 



tude of 400 m.. 



a beech forest 

 following resul 



TABLE H. 



Temperature 



At surface . 



One half foot below surface 



In the woorl 



Max. 



21.5 

 18.4 



Min. 



2.5 



SOIL TEMPERATURES 



In the open 



Max. 



28.6 

 24.5 



Min. 



.6 



* The Germination of Hydrastis canadensis. Rept. Mo. Bot. Gard. 

 18:85. 1907. 



t Ebermayer, E. Die physikalischen Einwirkungen des Waldes auf 

 Luft und Boden, etc, 1. Aschaffenburg. 1873. — Temperatures in 

 degrees of the Centigrade scale. 



r 



