132 



Dr. A. I>. Wall.-r. 



Other plants. Leaves of Tropseolum and of Mathiola, as far as I have- 

 yet seen, give a response to light, that is in the main the contrary of 

 the ordinary Iris response, viz., " positive " during illumination, and 

 subsequently " negative."* 



Li- 



0-01 



I hour us 



FiO. 4. Series of Normal Responses of Mathiola annua ("positive" during illu- 

 mination, subsequently " negative.") (1793.) 



Leaves of Nicotiana reacted like Iris. 



Leaves of Begonia have given a variety of responses strongly sug- 

 gestive of the simultaneous action of two opposed forces effecting a 

 resultant deflection in a + or - direction. 



As regards Mathiola and Tropaeolum, leaves empty of starch have 

 acted better than leaves laden with starch. 



Leaves of Ulva gave no distinct response (only one series of trials). 



Leaves of ordinary garden shrubs and trees, &c. (e.g., Lilac, Pear,. 

 Almond, Mulberry, Vine, Ivy), and petals of flowers, gave no distinct 

 response. 



Anesthetics. I was able to make only three satisfactory experi- 

 ments with Iris leaves, before the supply of available material had 

 come to an end.t 



The first was made upon a vigorous young leaf on May 15th, the test 

 (five minutes' illumination) being made at intervals of rather more 

 than half an hour, with the following result : 



* " Negative " as tbe term is employed in physiological literature, /.., negative 

 pole of positive element (" rincative "). 



t Note added July 16th. I have made further trial of anesthetics during the 

 past month upon leaves of Begonia. The effect vas perfectly clear, but slow viz. r 

 temporary abolition of response by ether vapour, permanent abolition by chloro- 

 form vapour, augmentation by " little " CO S , temporary suppression by " much " 

 CO). I think it possible that the refractory behaviour of the Iris leaf mentioned 

 in the teit may have been due to a primary effect of the anaesthetic upon stomatal 

 guard-cells. ( ride ' Proc. Physiol. Soc.,' June 30.) 



