I 4 4 PLANT PHYSIOLOGY 



exhaustive researches on the subject, must have carried out his experiments 

 in very impure air, may be deduced from his own statements (1906). Since 

 it is impossible to say what part this factor played in other researches, it would 

 appear to us useless to go into the results previously obtained by MOHL (1856), 

 MULLER-THURGAU (1876), VOCHTING (1888), and NOLL (1892), and to attempt 

 a discussion of the question as to whether the effect of one directive force on 

 the other makes itself evident at the perceptive stage, in the excitation or 

 only in the response. 



478, Lecture XXXVII is XXXVI of the 2nd German Edition, and, under 

 title of THERMOTROPISM AND OTHER TROPISMS, begins with last 

 paragraph on p. 478. 



479, 1. 45, for can be fully read can be somewhat more firmly 



480, 11. 28-42, for Obviously, growth . . . WORTMANN read Since we do not 

 know whether we have to deal with a difference of temperature in the indi- 

 vidual cells or in the entire organ, it is impossible to say how great the differ- 

 ence in temperature must be before the liminal intensity of the stimulus is 

 reached. Nor have any investigations been made as to how the height of 

 the absolute temperature affects the stimulus threshold or how the stimulus 

 increases as the temperature rises. There is ample room here for experimental 

 inquiry. 



As to the purely physical or chemical action of heat which leads to per- 

 ception we know nothing. It is not very probable that thermotropic percep- 

 tion is fundamentally similar to geotropic perception ; one of the facts which 

 WORTMANN 



481, 11. 26-7, for in all probability . . . XLIII). read in all probability it is 

 some effect induced by the current that is perceived. It has not as yet been 

 clearly made out whether we have to deal with a unilateral injury to the root 

 apex, as GASSNER (1906) thinks, or a local accumulation of electrolytic decom- 

 position products, as BRUNCHORST (1884) and EWART (1905) assume. If the 

 first view be correct, galvanotropism would be allied to traumatotropism ; if 

 the latter, the phenomenon should be associated with chemotropism, of which 

 we have now to speak. 



1. 39, after Fungi read (compare, however, FULTON, 1906) 

 1. 52 P. 482, 1. 9, for Whenever . . . current, read The fungal hyphae 

 then grew in the direction of the diffusion flow and toward the greater con- 

 centration . 



482, 1. 44, for doubfully read doubtfully 



1. 54 P. 483, 1. 2, for The determination . . . concentration ? read Just 

 as in heliotropism we established, in addition to a liminal intensity for uni- 

 lateral stimulation, a liminal intensity for bilateral, but unequally vigorous, 

 stimulation, MIYOSHI has also investigated, in the case of chemotropic stimulus, 

 how great the difference in concentration must be, if the same stimulant 

 operates on a fungal cell from two sides. 



483, 1. 23, after XLIII, p. 542). read 



The question now comes to be whether MIYOSHI 's experiences from 

 stimulation on two sides may be applied to stimulation arising from a single 

 diffusion flow. Does the cause of stimulation in this case also lie in the fact 

 that the side of the fungus hypha nearer to the diffusion centre borders on 

 a higher concentration of the stimulant than the opposite side ? It can scarcely 

 be conceived that in a diffusion area with constant flow the fall in concentra- 

 tion can be so rapid as to sink from 5-10 on one side to I on the opposite side 



