13 



but very few small green globules on the inner surface, and 

 therefore has then a faded appearance. The terminal joints 

 of these plants are still, however, as beautifully green as the 

 fresh plants, let them remain ever so long in darkness ; and the 

 motion in their cells ceases only at death. 



M. Dutrochet placed a Char a in water from which the air 

 had been extracted, and closed the tube under mercury ; the 

 circulation continued even under these circumstances for 

 twenty-two days, and ended only with the life of the plant ; 

 the effect therefore was almost analogous to that produced by 

 a complete absence of light. Corti had previously observed 

 that the circulation of the sap in Chares became slower when 

 the plants were placed in oil or in milk. Corti placed some 

 Charce in the receiver of an air-pump, and, rarifying the air 

 as far as possible, left the plants in this situation during forty- 

 eight hours. The circulation had discontinued ; but after the 

 plants had been placed in fresh water, it began anew in the 

 space of from eight to twelve hours. 



M. Dutrochet has also attentively observed the influences 

 of mechanical causes on the circulation in the Chares. Every 

 pressure and every mechanical irritation of the cells produce 

 a momentary decrease in quickness, and even a complete cessa- 

 tion of the circulation, which is, however, soon restored, the 

 effect being entirely proportioned to the force of the action. 

 Actual injury of the membrane, even by the point of a needle 

 only, causes a sudden cessation of the motion, w r hich then 

 never returns. Injuries have precisely the same effect on 

 Charce as on other plants in whose cells similar circulations 

 occur. If we cut off a single branch of a Char a, the motion 

 ceases for a long time in the adjacent cells ; in Vallisneria in- 

 deed this frequently lasts for ten to twelve minutes, until the 

 motion in the cells of the prepared section again recom- 

 mences with perfect activity. M. Dutrochet states that he 

 has also observed that the simple cell of the Chara exhibits 

 slight convulsive motions if one of the knots of an internode 

 be pierced, and when the outer cortical membrane is pared 

 off. In these cases also, the series of green globules are as- 

 serted to be the cause of the motion, for they are said to con- 

 tract at times in a zigzag direction, similar to muscular fibre, 

 while the membrane of the cell takes no part in this. I have 



