78 THE PLANT WORLD 



drums which move in accord with the expansion and contraction of the 

 fluid (kerosene oil) which fills the thermometer tube and drums. The 

 movement is transferred to a lever which writes the record on a revolv- 

 ing cylinder after the manner of an ordinary thermograph. The records 

 reported upon were obtained by burying the bulb at a depth of one foot, 

 and had been carried along for fourteen months at the New York Botan- 

 ical Garden. 



The maximum daily temperature of the soil occurs between 8 and 11 

 p. M., and the minimum between 8 and 10 a. m. Since the most favor- 

 able temperature for the absorption of water by roots is above the tem- 

 peratures actually recorded, it follows that the conditions for the absorp- 

 tion by roots of water from the soil is most favorable when plants least 

 need it, viz, at night, and least favorable when they most need it, i. e., 

 nearing mid-day. This helps to explain the great amount of water 

 excreted by plants, as from grass leaves. 



During any twenty-four hours throughout a year the greatest amount 

 of variation was only 2° C. (3.6° F.), and this only twice. The least 

 daily variation occurred in winter and was 1° C. (1.8° F.). From this 

 it is seen that the upper parts of plants are subjected to very much 

 greater temperature variations than the roots, and the whole relation of 

 leaf activity to root activity is thereby affected. Thus, the warming 

 of the sap as it rises alters its ability to hold in solution the salts and 

 organic materials. Descending currents, with organic substances from 

 the leaves, meet reversed conditions. 



It is, further, of very great interest to know that, after December, the 

 soil conditions become increasingly more favorable for root activities. 

 The temperatures are little lower in February than in April or May, 

 when the pushing out of new parts above ground is at its maximum. 

 Comparative studies of different localities will certainly be of interest. 



A THOROUGHLY good piece of physiographic ecology has been done by 

 Professor W. F. Ganong, whose results have appeared in the Bota?iical 

 Gazette * Of recent years there has been a very considerable amount of 

 attention given in the schools to geographic ecology, and the later text 

 books designed for the high school have contained elementary presenta- 

 tions of the subject. While I, for my own part, do not believe that much 

 of value can be done in this direction with high school pupils, neverthe- 

 less, a few things may be done well. This is, however, contingent upon the 

 knowledge and experience of the teacher. But up to the present time 

 comparatively few teachers have had the opportunity to study physio- 

 graphic ecology under the guidance of a competent instructor. For 

 such a summer's careful self-instruction might very profitably be under- 



* " The Vegetation of the Bay of Fundy Salt and Diked Marshes ; an Ecological Study." Botanical 

 Gazette, September to December, 1903. 



