. Carnegie Institution of Washington publication. ARID PORTIONS OF SOUTH AUSTRALIA. 29 (° C.) for the entire month of ; Even higher temperatures of superficial soils have been reported (Coville and MacDougal, q. v., p. 41). Therefore, at one and the same moment the roots of spe- cies of deeply penetrating root-habit may, near Tucson, be subject to a temperature stress of ° F. (183° C.) or over, or more than the total maximum yearly variation at a depth of 30 cm. Owing to the large number of factors which determine the tempera- ture of the soil, it is impossible, in the absenc
. Carnegie Institution of Washington publication. ARID PORTIONS OF SOUTH AUSTRALIA. 29 (° C.) for the entire month of ; Even higher temperatures of superficial soils have been reported (Coville and MacDougal, q. v., p. 41). Therefore, at one and the same moment the roots of spe- cies of deeply penetrating root-habit may, near Tucson, be subject to a temperature stress of ° F. (183° C.) or over, or more than the total maximum yearly variation at a depth of 30 cm. Owing to the large number of factors which determine the tempera- ture of the soil, it is impossible, in the absence of actual temperature- measurements, to satisfactorily adjudge this important feature of the physical environment of plants. Hann (1903:43) states that the daily variations in temperature hardly extend one meter into the ground, and that one observation daily at greater depths suffices to give good means. Conversely, all things being equal, it should be possible to roughly evaluate the mean annual temperature of average soils at a depth of one meter from the air means of the latitude. At the middle and higher latitudes, however, Hann states that the soil at a depth of one meter has an annual mean about 1° C. above that of the air. Taking the annual average temperature of the air for Australian regions along 135° east longitude, as given by Taylor (19182:4), we have, therefore, an estimate of the mean annual temperatures of the soil at a depth of one meter and at different latitudes. These are given in table 8, adapted from Taylor. It will be seen that at the depth given and -75° T5°- 70°. 55' FIG. 96.—Mean temperature of Australia for July, after Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Carnegie Institution of Washington. Washington, Carnegie Institution of Washington
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