1914] ECKERSOX— THERMOTROPISM OF ROOTS 255 



tures, that is, above 35 or 40 C. The one exception he found 

 was Phaseolus multiflorus, which gave negative curvatures from 

 22 to 50° C, but no curvature below 22 . The secondary roots 

 of P. multiflorus reacted positively at low and negatively at high 

 temperatures. Wortmann thought, therefore, that the primary 

 roots must have a positive thermotropism, although he was not 



demonstrate 



Helianthus 



Sinapis alba. In the first three species he observed 



only negative thermotropism; while Sinap 



• . • 



from 1 4 to 29 



tern 



thermotropic 



peratures. Porodko (7) studied the 



roots at temperatures from 40 to 70 C. He obtained negative 



curvatures and thought therefore that roots have only negative 



thermotropism. 1 



INVESTIGATION 



Method. — The apparatus used is a modification of Ganong's 

 differential thermostat. 2 A zinc trough, 20 inches long, having a 

 zinc box attached at each end, was heated at one end by an electric 

 coil and cooled at the other end by a freezing mixture. This gives 

 a fairly even gradation from 58 to 5 C. The electric coil has low, 

 medium, and high adjustment, so that the temperature gradient in 

 the trough can be increased or diminished as desired. Three such 

 thermostats were in use at one time. 



The seedlings chosen for this study were Raphanus sativus and 

 Pisum sativum. The trough was filled with sterilized Sphagnum 

 This was found to be the best medium, since in it the roots grow 

 perfectly straight. Seeds were sown in the trough at definitely 

 spaced intervals. When the roots were 1.5-2 cm. long, the ther- 

 mostat was brought to the He<sired temneratiires and the resnonse 



In 



w 



OOKER 



Thermotropism in roots, Plant World 17: 135-153. 1914) obtained no reaction in roots 

 set in 1 . 25 per cent agar. He concluded, therefore, that the curvatures of roots when 

 grown in sawdust, as in the work of Wortmann and Klercker, are due to hydrot- 

 ropism. The methods of experimentation used are subject to criticism and the 

 conclusions are erroneous. 



2 GxNONO, \\\, Plant physiology, p. 207. 1908. 



