904 TBANSACTIONS OF SECTION K. 



Correspondingly, be has been able also to show that even ordinary plants 

 exhibit the excitatory reaction by motile response. 



By the employment of modes of investigation, both mechanical and electrical, 

 he demonstrates the occurrence of two opposite responsive reactions, which are 

 de6nite under definite conditions. The true excitatory reaction is associated with 

 a negative turgidity-variation, contraction, and galvanometric negativity ; while 

 as a result of ' indirect ' stimulus, or increase of internal energy, the responsive 

 reaction is of positive turgidity-variation, expansion, and galvanometric positivity. 



The author finds, further, that the tonic condition of the tissue is also a factor 

 in determining the character of response. When the tissue is in a state of sub- 

 tonicity on the one hand, or of fatigue on the other, the sign of normal response 

 is apt to become reversed. 



By mechanical and electrical tests alike the author is able to demonstrate that 

 there is true transmission of excitation in plants, distinct from the propagation of 

 hydro-mechanical disturbance. The fibro-vascular elements provide preferential 

 channels, through which the wave of true excitation is conducted. 



The velocity of transmission of excitation increases with the intensity of 

 stimulus. A moderate rise of temperature is also conducive to the enhancement 

 of this velocity. Cold, fatigue, and the action of anaesthetics, on the other hand, 

 retard or abolish the conducting power. 



The character of that effect of stimulus which is transmitted to a distant point 

 depends on the conductivity of the tissue, and also on the intensity of the stimulus. 

 The eflPect transmitted is of negative sign when the stimulus is strong or long- 

 continued, or the tissue highly conducting. Conversely, it is of positive sign 

 when the stimulus applied is feeble, or the tissue semi-conducting. 



The fact that true conduction of excitation takes place in the plant, as in Jhe 

 animal, receives conclusive demonstration from the polar effects of currents on 

 excitation. The author finds that as in the animal, so also in the plant, the 

 normal effect is that the kathode excites at make and the anode at break. 



He has also observed the phenomenon of multiple response in vegetable tissues 

 under strong stimulation. A continuity exists in plants as between this multiple 

 and the so-called ' autonomous ' response. 



The characteristics of rhythmic tissues in the plant are found to be parallel to 

 those of rhythmic tissues in the animal. 



The author has also been able to determine with accuracy the death-point of a 

 plant. A mechanical and electrical excitatory spasm is shown to occur at the 

 initiation of death. In the morographic record the critical point is exhibited as a 

 sudden inversion of the curve. 



6. The Mechanism of Mitosis. By W. L. Balls. 



7. A perfectly Fertile Species-hybrid showing Segregation. 

 By Dr. J. P. Lotsy. 



8. The Natural Crossing of the Cotton Plant, By W. L. Balls. 



FRIDAY, SEPTEMBER 4. 



The following Papers were read : — 



1, Photo-chemical Action in the Test-tube and the Leaf, 

 By Dr. F. F. Blackman, F,R.S. 



