146 HENRY D. HOOKER, JR. 



the roots were immersed in this, and again no reaction was ob- 

 tained. Later experiments showed that roots grow very poorly 

 and sometimes not at all in such a mixture because of the absence 

 of oxygen. 



The right half of the shallow glass jar was filled with moist 

 sawdust, such as was customarily used to sprout the seeds. The 

 other half was filled in the same way with very dry sawdust. Seed- 

 lings of Lupinus albus were planted in the plane between these 

 two vertical layers. After six hours, three of the ten seedlings so 

 planted had wilted, two were straight and in good condition, while 

 the other five had bent into the moist sawdust. The experiment 

 was repeated with even better results, as this time eight of the 

 ten grew sideways into the moist sawdust. 



For the remaining experiments small zinc cases were used, 17 

 cm. long, 2 wide and 6 high. One side was cut out, and a piece 

 of glass substituted. To render the tank waterproof, plastolinum 

 was pressed into the cracks between the glass and the zinc. A 

 1.25 % solution of agar-agar in water was tried and found very 

 satisfactory as a medium for roots to grow in because it is soft 

 enough to allow the roots to bend in it and yet firm enough to 

 preserve a solid consistency. The rate of growth in this medium 

 averaged 2 mm. for every three hours. The mixture was poured 

 into the zinc tanks while still hot. When it had become solid on 

 cooling, holes were made with a glass needle, and the rootlets 

 to be experimented on were carefully inserted in them. This was 

 usually done under water, to avoid the entrance of air with the 

 roots. The sawdust in the large tank was then cleared away 

 froiii the outer side that was to be heated, and the can with agar- 

 agar put in its place, with the glass wall facing inward. It was 

 covered in and packed down on all sides with the moist sawdust. 

 In this way the roots were placed in the same position that they 

 had in Wortmann's thermo tropic experiments, ahgned a few milli- 

 meters from the wall, with T', which was now inserted in the 

 agar-agar. The sole difference rested in that the roots were now 

 surrounded with agar-agar instead of the moist sawdust. Obser- 

 vations of the progress of the experiments were easily made by 

 removing the can, as the roots were visible through the agar and 

 the glass wall. The solution proved to transmit the heat as read- 



