of the ground, being protected from mechanical injury by 

 being placed in a grooved board. A narrow trench 2 meters 

 long and about 20 centimeters in depth was dug and was then 

 prolonged in a tunnel to a farther distance of 50 centimeters. 

 This tunnel was only large enough to receive the bulb, and 

 after that had been pushed to the farther end of the tunnel the 

 excavated soil Avas packed around it in a manner as nearly 

 natural as possible. By this arrangement the layer of soil 

 above the bulb was left undisturbed and artificial drainage 

 conditions were not introduced. This arrangement brought 

 the upper surface of the bulb in contact with the soil pene- 

 trated by the matted roots of grasses and other small herba- 

 ceous plants, which also extended much deeper around the 

 excavation. 



The greater bulk or volume of the root system of the smaller 

 plants usually lies nearer the surface of the soil than the posi- 

 tion of the bulb of the thermograph, but the important func- 

 tion of absorption is carried on chiefly by the younger, most 

 recently formed terminal portions of the roots which lie deeper 

 in the soil. The rate at which mineral and other substances 

 in solution in the soil are taken up, the permeability of the 

 protoplasmic membranes, the turgidity and consequently the 

 rigidity of the roots are also greatly affected by temperatures, 

 while the growth of these organs, together with their endur- 

 ance and that of all underground organs, depends not only 

 upon the actual temperatures encountered, biit also upon the 

 rapidity with which changes ensue. 



Before being placed in position the air thermograph and 

 the soil thermograph were placed in a closed room with a 

 standardized mercurial thermometer (No. 2792, G. S. Keichs- 

 Anstalt, Berlin), and were found to read alike to within a 

 small fraction of a degree, allowing for a slowness of response 

 by the thermographs. 



The records on hand now embrace a period of fourteen 

 months, and the facts obtained seem to be of sufficient inter- 

 est to warrant their discussion at the present time, together 

 with some of the actual curves traced by the instruments. 



It may be seen from these that the maximum daily tempera- 

 tures occurred between 8 and 11 p. m., and the minima twelve 

 hours later, or between 8 and 10 a. m. The optimum tem- 

 perature for absorption by roots lies well above that of the 

 soil at the depth at which the observations were made. It 

 follows, therefore, that the temperature of the soil approaches 

 this optimum most nearly, and offers most favorable condi- 

 tions for the taking up of watery solutions at a time of the 

 day when the amount of water thrown off by the shoot and of 

 mineral matter used in metabolism are nearing the minimum 

 by reason of the absence of light, lowered air temperature, 

 and consequent increased humidity of the air. These inhar- 

 monious conditions account almost wholly for the profusion 

 of guttation excretions or " dew drops " formed on the tips 



