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1902J CURRENT LITERATURE 463 



retained in a modified form, when the present extreme revulsion of the Eng- 

 hsh school of anatomists from the epoch-making anatomical hypotheses of 

 Van Tieghem has reached a condition of equilibrium. 



The present work has resulted in the discovery of cambial activity in the 

 parenchyma between the phloem and xylem of bundles in the young stem, 

 which brings about the addition of fresh elements to the xylem. The authors 

 discuss the parallel first instituted ])y Mettenius between the root-traversed cor- 

 tex of the marattiaceous stem and the somewhat similar tissue present in the 

 fossil genus Psaronius, They conclude that the two are not really comparable 

 and suggest that in Psaronius the tissue in question results from the fusion of 

 roots which are already outside the stem. — E. C. Jeffrey. 



A NEW METHOD of Studying the irritability of plant protoplasm has been 

 devised and quite extensively applied by Bose^-*. It depends upon the exist- 

 ence of electric responses due to stimulation. As in animal muscle and 

 nerve, if a limited portion of a plant tissue be injured in any way, there is pro- 

 duced a difference of electrical potential between the injured and the unin- 

 jured part, and a ** current of injury" results, the injured region being 

 positive with reference to the remainder of the tissue. In the case of ani- 

 mals a stimulus applied to a tissue exhibiting this current of injury causes a 

 momentary but well-marked diminution in the current. A current of response 

 or " action current " is produced which flows from the more active (uninjured) 

 portion to the less active (injured) portion, thus producing a depression in the 

 preexisting current of injury. This phenomenon, known in animal physi- 

 ology as " negative variation, " is found by Bose to occur quite generally in 

 plant tissues. Stems, leaf stalks, flower stalks, and roots of various plants 

 were used in the experiments. To produce the current of injury a slight 

 burn with a potash solution is sufficient. For the negative variation a sharp 

 mechanical blow upon the tissue or a slight torsion about its long axis was 

 used. Records of the response were taken in the form of curve tracings, 

 partly made by hand upon a revolving drum following the migrations of a 

 beam of light reflected from the galvanometer, and partly recorded automat- 

 ically by this beam upon a sensitive photographic plate. The response is 

 found to be determined quantitatively by the intensity of the stimulus produ- 

 cing it, but some tissues {e.g., leaf-stalk of turnip, celery, cauliflower) show 

 fatigue if a uniform stimulus is repeated too often, and some show the 

 so-called '* stair-case effect" known for certain animal tissues. 



Another and better method for investigating these phenomena obviates 

 injury. The tissue to be tested is fixed firmly at a point between the two 

 electrodes and a stimulus is applied on one side of the block thus produced. 

 This stimulus (a blow or a torsion) is of course thus confined to the portion 

 of the tissue on its own side of the blocking clamp, and a current of response 



'* Bose, J. C, Electric response in ordinary plants under mechanical stimulus. 

 Jour. Linn. Soc. Bot. 35 : 275-304. /^x. 2^. 1902. 



