NUTRITION. 



87 



rents of the other cells ; and there is no separating me- 

 dium between the upward and downward streams of 

 each cell individually, although they continue perfectly 

 distinct from each other, and whatever may be the po- 

 sition of the plant, preserve their original direction. 



69. The rapidity of the streams varies according to 

 the age of the plant, and its vegetative vigour and 

 warmth has much influence upon it ; a range of tempe- 

 rature between 53 Fah. and 77 is most favourable for 

 its continuance, according to Du Trochet. 



70. Besides the existence of streams of rotation in 

 the plants we have described, they are likewise to 

 be seen in many of the higher orders; but the di- 

 rection of the streams though taking place in closed 

 cells is somewhat different to that seen in Chara, and by 

 Schultz they are considered of an entirely different nature. 



71. This modification of rotation is well seen in 

 Tradescantia virginica, and may be il- 

 lustrated by the following description 



from Meyen. The annexed figure repre- 

 sents three cells from the stem of Trades- 

 cantia ciliata ; in the cell a b, the most 

 simple form of rotation is seen in a single 

 stream of a spiral direction running from 

 c to d, where it turns round and runs to 

 the nucleus e, passing along the other 

 side of the cell to f\ in g h there is a 

 point especially to be noticed, the fine 

 stream running from i to k, and which at 

 I runs at the end of the cell, gives off 

 some fine molecules and other matter, 

 which take upon themselves a distinct 

 rotary motion independent of that of 

 the main stream, as is marked by the 

 arrows ; this separated rotation does not, 

 however, last long, but returns to the 

 original stream. In / m small streams 

 are seen connecting the two main streams 

 together, and meeting at the nucleus. 



