RECENT ADVANCES IN SCIENCE 397 



from which it is concluded that ether narcosis only suppresses 

 the power of perception of the stimulus but does not affect the 

 power of reaction. Like contact stimulation, stimulation by 

 wounding often results in more rapid growth, but if the stimu- 

 lation is too strong cessation of growth may result. 



An interesting suggestion is made by Ricca (Nuovo giorn. 

 bot. itaL, 23, 51 -171, 191 6) as to the mode of propagation of 

 the stimulus in Mimosa. After showing by ringing experiments 

 that the stimulus is propagated in the wood, it is further shown 

 that the stimulus is propagated through a damaged zone, or 

 even if the continuity of the tissues is completely interrupted 

 and two parts of a branch joined by a tube of water. This 

 suggests that the stimulus is propagated by means of a substance 

 formed in the protoplasm which is carried through the plant 

 in the water channels by the water current, and which acts as a 

 stimulus when it reaches the pulvini. Further evidence in 

 support of this theory was obtained by cutting sections of the 

 stem and allowing the contents to diffuse out into a small 

 quantity of water, which on absorption by cut branches of the 

 stem, produced the characteristic stimulation. As in Loeb's 

 work with geotropism in Bryophyllum cited earlier, a com- 

 parison with hormones is suggested. 



Some observations of Bose and Das (Proc. Roy. Soc. London, 

 B, 89, 213-31, 1 91 6) indicate that under different conditions 

 the excitability and conductivity in the case of stimulation of 

 Mimosa vary. Fatigue may be induced in the same way as in 

 animals. 



Leaf movement in the case of insectivorous plants has been 

 investigated by W. H. Brown in the case of Dioncea, and by 

 H. D. Hooker in Drosera. In the former Brown (Amer. Journ. 

 Bot. 3, 68-90, 1 91 6) concludes that closure of the leaves is 

 brought about by increase in size of the ventral cells owing to 

 stretching of the cell walls. This increase in size is permanent, 

 and opening of the leaf results from a similar growth of the 

 dorsal cells of the leaf. The enlargement of the ventral cells 

 the author explains on the ground of their increased osmotic 

 concentration following on stimulation. In Drosera Hooker 

 {Bull. Torrey Bot. Club, 43, 1-27, 191 6 ; 44, 389-404, 191 7) 

 found that during bending of the leaves the osmotic pressure 

 decreases in the cells on the concave side, but remains unaltered 

 on the convex side, and the author concludes that this decrease 



