142 HENRY D. HOOKER, JR. 



Although not included in his subject, Steyer repeated Wortmann's experiments 

 with Lepidiurn sativum and Zea Mays, making use of his improved apparatus. 

 The first leaf of the epicotyl was found to be really thermotropic in conformity 

 with the results obtained by Wortmann. 



More recently there has appeared an article by PohP^ discussing the thermo- 

 tropism of flax. This shows strong resemblances to Anemone stellata, since it 

 is positively thermotropic when acted on at ordinary temperatures, as by the 

 sun's rays for instance. At excessively high temperatures it reacts b}^ negative 

 thermoh'opism. 



In a series of articles called "Vergleichende Untersuchungen fiber die Tro- 

 pismen," Porodko" discusses among others negative thermotropism. He worked 

 in the temperatures ranging chiefly between 40° and 70°C. but ranging as high as 

 250°C. There could be no question of the confusion here of traumatropism or 

 wound stimulus for thermotropism, as Porodko himself admits in the fifth paper of 

 the series, which appeared onlj' last June (1913). These results therefore need 

 hardly concern us in this discussion. 



EXPERIMENTATION 



Method. For the experiments with thermotropism, the appa- 

 ratus described by Wortmami was used. This was a zinc tank 20 

 cm. long and 14 cm. square on the end. A soldered zinc partition 

 divided this lengthwise into two unequal compartments, the one 

 8 and the other 6 cm. wide. In the outer wall of the former, a 

 short brass tube was soldered in the middle near the bottom, 

 which w^as to serve as an inlet. On either end of this wall near. the 

 top, two more tubes were inserted to serve as outlets. These were 

 connected by rubber tubes to the water supply, so that tap- 

 water circulated continually through this compartment. The 

 temperature was practically^ constant at 12°C., thus effectually 

 cooling off the partition dividing the tank. The other compart- 

 ment was filled with moist loose sawdust, like that in which the 

 seeds were germinated. Its outer wall was besmeared on the out- 

 side with soot, and heated by a specially arranged fixture. This 

 consisted of a T-shaped brass tube, the cross of which w^as 22 cm. 

 long and closed at both ends. This was punctured by six holes, 



1^ Pohl, J., Der Thermotropismus der Leinpflanze. Beih. Bot. Cen. 24»: 111-131, 

 1909. 



^* Porodko, Th. M., Thermotropismus der Pflanzenwurzeln. Ber. d. Dcut. Bot. 

 Ges. 30: 305-313, 1912; Das Wesen der traumatropen Erregung bei den Pflanzen- 

 wurzeln. Ber. d. Deut. Bot. Ges. 30: 630-641, 1912. Das mikroscopische Ansehen 

 der tropistisch gereizten Pflanzenwurzeln. Ber. d. Deut. Ges. 31: 248-256, 1913. 



