THERMOTROPISM IN ROOTS 143 



spaced at intervals of 3 cm. The stem of the T was connected by 

 a lead tube to the gas fixture, which permitted necessary manipu- 

 lation and free movement. The six jets of flame of equal size 

 issuing from the six equidistant punctures in the head of the T 

 were arranged parallel to the sooted wall near the bottom. By 

 varying the distance from the wall, the temperature could be reg- 

 ulated. In this way the outer wall of the sawdust compartment 

 was heated uniformly, or ver}' nearly so, throughout its length. 

 The completed apparatus thus produced a constant and perma- 

 nent difference of temperature in the saw^dust. To measure the 

 temperature, Wortmann used three thermometers, one near the 

 cold partition, one in the middle and the third near the heated 

 side. These were shoved into the sawdust an equal distance from 

 the two ends of the tank. The thermometer by the outer w^all was 

 for convenience designated as T' , that one in the middle as T" and 

 the third one near the cold partition as T"". In the present ex- 

 periments the same arrangement was followed except that the 

 middle thermometer T" was omitted. A zinc cover was cut 

 to cover the sawdust and provided with two holes for the other 

 thermometers. 



The details of the method were in all essential respects identical 

 with those mentioned by Wortmann. It may be specially em- 

 phasized, however, that the roots were always so placed that the 

 thermotropic difference acted on their flanks. As all the roots 

 in a given experiment were placed in the same relative position, 

 this saved the trouble of marking the roots to know which side 

 had been exposed to the heat, as was occasionally necessary. 

 Special care was also taken to avoid geotropic reactions, which 

 might injure the results in case of carelessness in transferring the 

 seeds from one place to another. The roots were found to react 

 best in rather moist sawdust. 



Ervum, Pisum, Phaseolus, and Zea were selected for the experi- 

 ments with agar-agar, because Wortmann had used these, and 

 had based all his conclusions regarding themotropism on their 

 behavior. Lupinus was also used. 



Experiments. The experiments which Wortmann made with 

 roots (loc. cit.) were repeated with Ervum Lens and Lupinus albus. 



