=103. Temperature curves.= The kinds and combinations of temperature curves are almost without number. The simple curves of most interest are those for a series of stations or habitats, based upon the level of three feet, or the surface, or the daily mean. The curves for each station representing the different heights and depths and the season curve of the daily means for a habitat are also of much importance. One of the most illuminating combinations is that which groups together the various level curves for a series of habitats. Other valuable combinations are obtained by grouping the curves of daily means of different habitats for the season, or the various station curves. =104. Plant temperatures.= The direct effects of temperature as seen in nutrition and growth can be ascertained only by determining the temperature of plant tissues. The temperatures of the air and of the soil surface have an important effect upon humidity, and water-content, and through them upon the plant, but heat can influence assimilation, for example, only in so far as it is absorbed by the assimilating tissue. The temperatures of the leaf, as the most active nutritive organ of the plant, are especially important. While it is a well-known fact that internal temperatures follow those of the air and soil closely, though with varying rapidity of response, this holds less for leaves than for stems and roots. Owing to the very obvious difficulties, practically nothing has yet been done in this important field. A few preliminary results have been obtained at Minnehaha, which serve to show the need for such readings. Gravel slide rosettes in an air temperature of 24° C. and a surface temperature of 40° C. gave the following surface readings: _Parmelia_, 40°, _Eriogonum_, 38.6°, _Arctostaphylus_, 35°, _Thlaspi_, 31.8°, and _Senecio_, 31°. The leaf of _Eriogonum flavum_, which is smooth above and densely hairy below, indicated a temperature of 31.8° when rolled closely about the thermometer bulb with the smooth surface out, and 28° when the hairy surface was outside. The surface readings of the same leaf were .5°–1° higher when made upon the upper smooth surface. This immediately suggests that the lower surface may be modified to protect the leaf from the great heat of the gravel, which often reaches 50° C. (122° F.). PRECIPITATION