Prof. F. Cohn on the Contractile Tissue of Plants. 191 



of the filaments independently of the operation of external ex- 

 citants is a consequence of the drying up of their tissue ; but 

 such is not the case. 



13, 14. On the contrary, this shortening is a consequence of 

 an active process of contraction. That it does not depend on 

 desiccation of the organs, Cohn proved by contriving in some 

 experiments to keep them moist, and in others to immerse the 

 whole sexual apparatus in water. In the former series the 

 power of contractility remained, whilst in the latter their capa- 

 bility of rapidly shortening themselves on the application of an 

 excitant was almost instantaneously lost, though, after a time, it 

 gradually revived. 



15. From these experiments it was undeniably established 

 that the filaments have their maximum length at the epoch of 

 their highest irritability, and that subsequently they con- 

 tinuously and gradually contract, and also that this phenome- 

 non is not dependent on the hygroscopic conditions of the parts. 

 These facts necessarily imply that a direct relation subsists be- 

 twixt the contractility of the filaments, the loss of their irritability, 

 and the gradual death of their tissue. To demonstrate this, 

 Cohn subjected the prepared sexual apparatus of a floret to 

 ether, with the view of destroying its vitality by the vapour, 

 when he found that the filaments shortened themselves greatly, 

 whilst the style remained unchanged. To obviate the desiccating 

 effects of the ether-vapour on the tissue in this experiment, he 

 introduced water so as to keep the parts moist. 



16. Mechanical contact is not the only excitant to active con- 

 traction, but electricity is so likewise, and acts powerfully when 

 the current is transmitted through the sexual apparatus. More- 

 over, when the current is strong, the shortening is not succeeded, 

 as after ordinary stimulation of the filaments, by elongation; 

 on the contrary, their irritability is destroyed, and they remain 

 shortened. Parallel phenomena have been noted by Schlacht 

 and Pfiuger in the leaves of Mimosa pudica when an induction- 

 current traverses them ; and by Nasse in the stamens of Ber- 

 beris. The effects of a continued constant current Cohn has not 

 yet been able to determine. 



17. From the observations made, it is presumable that the 

 lasting and permanent shortening of the filaments, with loss of 

 irritability, is a symptom of its extinction, whether produced 

 rapidly by ether-vapour, by water, or by strong electrical action, 

 or whether it happens spontaneously and gradually. The short- 

 ening also appears in all cases, under similar circumstances, to 

 advance at a constant minimum rate, whatever may be the cause 

 of the extinction of irritability. 



The proximate active agent in the process of shortening is the 



