CIRCULATION IN PLANTS. 



375 



small tubes, and the incrustation of carbonate of lime is a 

 rare occurrence. A portion of the upper part of one of the 

 stems highly magnified is represented by fig. 246 ; in this the 



Fig. 245. 



Fis. 246. 



arrows denote the direction of the movement, and the letters 

 a a the colourless division of the joints which separate the 

 ascending and descending currents ; the circulation may even 

 be Ti^itnessed in the whorl of young leaves at the top, s, and in 

 all the other parts indicated by the arrows. 



Method of Viewing the Circulation. — If the Chara or Nitella 

 be in abundance, a new piece may be selected each time for 

 examination, but if it be scarce, and especially if it be wished 

 to watch its development, then the plan adopted by Mr.Varley 

 will be found necessary. For this purpose some cylindrical 

 wide-mouthed phials will be required ; into each one a small 

 branch of the plant must be put, then a thin slip of glass is to 

 be laid over it, and kept in place by two wedges of cork, in 

 the manner shown in fig. 247 ; water may now be added to 

 fill up the phial, and the plant is then ready to be examined. 



