THERMOTROPISM IN ROOTS 139 



the same results as did those in the Ervunt Len^. Wortiiuinu therefore extended to 

 roots generally the principle applied to sprouts, that the time required for the re- 

 action to appear is inversely proportional to the intensity of the stimulus. Zea 

 Mays gave positive reactions with great facilitj' and definition; the negative reac- 

 tions, however, were less distinct. Phasenlus: showed no positive thermotropism 

 whatever. 



Wortmann experimented also with decapitated roots, to determine if the root- 

 tip alone were capable of receiving and transmitting thermotropic stimuli. The 

 four species already mentioned were again used, and in every case they gave nega- 

 tive thermotropic reactions. The results were seriously interfered with by nuta- 

 tion, especially at lower temperatures, when thermotropic bending was practically 

 absent. 



Thermotropic experiments were made with secondary roots of Phaseolus mulli- 

 florns in an apparatus similar in all essential respects to the one used before, except 

 that it was smaller. After three or four hours negative bending was observed in 

 roots at a temperature of 38° to 40°C. After five hours more, positive bending 

 was seen in the roots at a temperature of 10°C. Only such roots came under con- 

 sideration that grew parallel to the sides of the apparatus and thus received the 

 heat stimulus on but one side. The reactions were not as vigorous as those ob- 

 served in roots of the first order. Wortmann criticises Barthelemy's experiments as 

 unscientific in method and valueless because of the want of particulars. 



In 1888, Voechting^ published an article concerning the thermotropism of mag- 

 nolia flower-buds, interesting because it substantiates Van Tieghem's theory. He 

 observed that buds of Magnolia Yulan and Magnolia conspicua Soulangeana often 

 bent to the north away from the rays of the slanting spring sun. That bending also- 

 occurred when the buds were covered with a black paper cap or with a glass bulb 

 painted with a solution of iodine in carbon bisulphide, showed that it was caused 

 by heat and not by light. A considerable difference of temperature existed between 

 the sunny and shady sides of the buds. Thermometers pressed against the outside 

 registered a difference of from 2° to 4o°C. Inserted between calyx and caroUa, they 

 showed a difference of 2.8° to 3.9°C., and between the inner and outer whorls of 

 petals, 1° to 2.2°C. If the nights were cold, the buds bent better, because growth 

 took place only during the day, when the thermotropic difference had effect. 

 Voechting endeavored to reconcile the conflicting evidence of Van Tieghem and 

 Wortmann by distinguishing between radiated and conducted heat. He suggested 

 that their effects might be different and might counterbalance each other. No deci- 

 sive conclusions, therefore, should be drawn from Wortmann's results as in his 

 experiments on roots both kinds were present. 



Two years later appeared another article by Voechting^" dealing with the effects 

 of heat on the movements of Anemone stellata peduncles. Three distinct phenomena 

 were observed : the straightening of the flower stalk in the morning and the resump- 

 tion of the sleeping attitude in the evening; the opening and closing of the flower; 

 and the following of the sun's course. Of these movements, all of which were found 



» Voechting, H.", tJber den Einfluss der strahlender Warme auf die Blutenentfalt- 

 ung der Magnolia. Ber. d. Deut. Bot. Ges. 6 : 167-178, 1888. 



'"Voechting, H., tJl^er den Einfluss der Warme auf die Bliitenbewegung der 

 Anemone stellata. Jahrb. wiss. Bot. 21: 284-292. 1890. 



