402 
ON THE FLUIDS OF PLANTS. 
greater or less extent. The relative changes this fluid undergoes during different 
seasons, and under varying atmospheric influence, have been made the subject 
of an ingenious series of experiments by Biot.* During the spring and summer, 
when the leaves are expanding, and performing their functions of exhalation, 
respiration, digestion, and formation of the fibres of the wood, the quantity of 
sap ascending is very great; but in the winter only enough sap seems to ascend 
to maintain the vitality of the plant. 
The general tendency of this motion of the sap is undoubtedly upwards, but 
it does not appear to be necessary to suppose that the particles of the fluid move 
directly upwards, or that they do not pursue a retrograde course before they 
reach their destination. If the phenomena of intercellular rotation were con¬ 
sidered a part of the general motion of the fluids of the plant, it would strengthen 
this supposition. 
A second motion is that of intercellular rotation, and is seen in the cells of 
Chara^ Nitella^ and other plants, and probably exists in the cellular tissue of all 
other plants. It has been supposed, that the fluid seen moving in these cells was 
confined to them, but from the resemblance of this motion to the general circula¬ 
tion observed in polypiferous animals, and from the structure of Ckara^ &c., not 
differing from other plants, it seems most consistent with analogy to refer this 
‘‘ rotation”, as it is termed, of the sap to the general movement of that fluid in 
plants. In fact it does not appear that the fluid in the cell rotates, but that 
minute globules in the cell are seen to ascend and descend in a rotatory 
manner. Whatever may be the extent of this intercellular rotation, its cause 
is very obscure. There is, however, one point connected with it to which 
I would allude here. It is the resemblance between this motion and those 
observed in the lower tribes of animals—the Polypifera and Poriphera. In these 
animals a similar motion of the fluids has been observed, and the resemblance 
between these motions and those produced by the cilise which have been lately 
observed to exist in many of the canals conveying fluids in animal bodies, has 
led some comparative anatomists to attribute them to the same cause.t The 
question I would propose, is—Can the motion in the cells of plants be referred to 
the action of minute invisible cilise ? 
A third kind of motion has been described by Schultz, as taking place in a 
peculiar kind of vessel which he calls vital vessels” or “ ducts of the latex.” 
Dr. Bindley thinks these vessels are nothing more than intercellular passages, 
and probably the fluid seen passing through them is only a part of the general 
motion of the fluids of the plant. 
His apparatus is described in Henslow’s Physiological Botany. 
f For all that is at present known on this subject, see an elaborate article on “ Cilice,” by Pro- 
fessor SiiARPEY, in the CyclopcBdia Anatomy^ &c. 
