THERMOTROPISM IN ROOTS 141 



he concluded that caloritropic phenomena are of complicated nature and are pro- 

 duced by at least two factors working antagonistically to one another. With the 

 help of mathematics, including a careful employment of integral and differential 

 calculus, he demonstrated that according to Van Tieghem's theory roots would 

 react more vigorously between the optimum and minimum temperatures than be- 

 tween maximum and optimum. The exact opposite is indicated by the graphs. 



Geotropism was shown to be an active factor opposing the action of caloritro- 

 pism. Their interaction accounts for the zig-zag shape, which he observed in numer- 

 ous roots, and which is due to the alternate action of these influences. Hia experi- 

 ments did not enable him to decide if hydrotropism or the action of air-currents 

 aflfected the caloritropic reactions, but he hoped to make special experiments to 

 throw light on this question. 



In 1901 Steyer^^ published a thesis dealing with the physiological aspects of 

 Phycomyces nitens. A critical study of its thermotropic relations was made and 

 Wortmann's experiments were repeated. He did not consider that Wortmann's 

 apparatus insured a constant temperature evenly distributed over the surface of 

 the plate used as a source of heat. Consequently he constructed the following ap- 

 paratus.- A zinc tank was made 20 cm. high, 20 cm. long and 7 cm. wide. Through 

 this hot water was allowed to circulate, which was heated in a closed vessel con- , 

 nected with the tank by means of two tubes. This kept the water in motion and in- 

 sured a constant temperature. The two ends and one side of the tank were packed 

 in felt. Against the other side, which was smeared with soot, a glass cylinder 

 20 cm. long and 12 cm. in diameter was shoved, and the connection made tight with 

 a felt ring. The other end was left open to secure a difference of temperature. As 

 the possibility of hydrotropic influence must be eliminated, the atmosphere was 

 kept as nearly saturated with moisture as possible. This was done by lining the 

 cylinder with wet filter paper and placing a glass plate 2 cm. from the open end. 

 This plate was also covered with filter paper and water flowed over it continually. 

 The spores were sown on cubes of bread. When the sporangiophores had developed, 

 the cubes were placed on mica plates and these put in the cylinder just before 

 the sooted zinc surface. Experiments lasted eight hours and were carried out in a 

 dark room. Steyer worked with temperatures varying from 13° to 33°C., but in no 

 case was he able to obtain thermotropic reactions. Although he tried sporangi- 

 phores of several ages the results were the same. 



He therefore concluded that Wortmann's results were due to hydrotropism 

 against which he took no precautions, aided by positive heliotropism. Cultures 

 placed before the heated zinc wall without the cylinder bend slightly away, show- 

 ing that they were negatively hydrotropic. This reaction was not strong enough, 

 however, to correspond to the results obtained by Wortmann. A consideration 

 of the apparatus used by him showed that the iron plate which acted as the source 

 of radiation, in all probability shut off considerable light, an error simply doubled 

 by the mirror. As the sporangiophores are positively heliotropic, as was shown 

 by other experiments, they naturally bend away from the plate, and more stronglj^ 

 the nearer they were to it. This experiment explained why Wortmann thought 

 the intensity of the reaction increased with the temperature. 



'^ Steyer, K., loc. cit. 



