CHAP. XI. 
CIRCULATION" OF THE SAP. 
327 
The former is what has been alluded to in the preceding ob- 
servations, the latter is altogether of a different nature. 
With regard to the latter, Corti, in 1774, Fontana, L. C. 
Treviranus, and especially Amici, have made some most cu- 
rious observations. It was said that if a portion of Chara 
flexilis, or of any of the transparent species, or of any crusta- 
ceous kind, the opaque cuticle of which is first scraped away, 
be examined, a current of sap will be distinctly seen in each 
cellule setting from joint to joint, flowing down one side and 
returning up the other, without any membrane intervening to 
separate the opposing currents ; each cellule has a movement 
of its own, independent of that of the cellules above and below 
it; sometimes the movement stops, and then goes on again 
after a brief interval ; if a cellule is divided into two by a 
ligature passed round it, a separate movement is seen in each 
of the divisions ; this motion is rendered distinctly obvious by 
the numerous minute green granules which float in the trans- 
parent fluid, and which follow the course of the currents. 
The observations of Amici have been verified in this country 
chiefly upon species of Nitella ; and from the investigations of 
Solly, Varley, and Slack, the nature of the phenomenon has 
been determined with considerable precision. 
Among other things, it has been ascertained that in Nitella 
the currents have always a certain relation to the axis of 
growth, the ascending current uniformly passing along the 
side of the cell most remote from the axis, and the descending 
current along the side next the axis. 
Similar motions have been seen in several other plants. 
In the cells of Hydrocharis Morsus-Ranas the fluid has been 
observed to move round and round their sides in a rotatory 
manner, which, however, has not been seen to follow any 
particular law. In the joints of the hairs of Tradescantia 
virginica several currents of a similar nature exist; and in 
the hair of the corolla of a species of Penstemon, Slack 
has observed several currents taking various directions, some 
continuing to the summit of the hair, whilst others turn and 
descend in various places, two currents frequently uniting in 
one channel. 
It may hence, possibly, be assumed that in the cells of 
Y 4< 
