12 



a Chara, and noticed the separation of the general circulation 

 thus caused ; an internode tied in three places exhibited four 

 distinct circulating currents, which even continued when the 

 adjacent parts were cut off. 



M. Dutrochet examined the influence of various tempera- 

 tures on the circulation in the Chares, and likewise noticed 

 that it still continues at the freezing point of water, but pro- 

 ceeds very slowly. But Corti had previously observed that a 

 cold of 2 to 5 killed the plants ; in general, however, we may 

 say that actual freezing kills the plants and causes the circu- 

 lation to stop. M. Dutrochet observed that the circulation 

 increased in rapidity with higher degrees of temperature, which 

 was the case up to 27 Cels. ; but he did not remark that not 

 only at one and the same temperature this motion varies ex- 

 ceedingly in the several cavities according to their different 

 ages, but that even in the cells of the so-called bark and in 

 those of the interior cavity the velocity in the circulation dif- 

 fers. On the application of a higher degree of heat, says M. 

 Dutrochet, the motion is at first somewhat slower, but gra- 

 dually rises, and finally arrives at the usual rapidity; but 

 water at 45 Cels. killed the plants irrecoverably. 



M. Dutrochet endeavours to show that the influence of light 

 is indispensably necessary to the preservation of the current 

 in the Charts, reasoning from views according to which light 

 is considered as the means for the fixing of the carbon from 

 the carbonic acid of the air. Light appears to me to exercise 

 no immediate influence on the circulation of the sap in the 

 cells of the Chara?, for I kept for several months plants of 

 Chara in a dark situation, carefully covered, but observed in 

 them, at a temperature of 7 to 8 Reaum., motions quite as 

 active as these plants exhibit in summer, even at a higher 

 temperature. M. Dutrochet placed several Charce in a per- 

 fectly dark situation, at a temperature of 14 to 20 Cels., 

 and observed that the motions of the sap became in most of 

 them slower, indeed discontinued completely within twenty- 

 four to twenty-six days in the younger plants, which had at 

 the same time faded. According to my own observation, this 

 fading of the Charce is quite peculiar ; the fact is, that the 

 cells of the outer cuticle decay and fall off, and then only 

 the inner membrane remains, which in C^. vulgaris exhibits 



