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 spiing 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 Polypi/era 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 ciliae 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.? The 

 question I would propose, is — Can the motion in the cells of plants be referred to 

 the action of minute invisible ciliae ? 



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. Lindley 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 " Cilia?," by Pro- 

 fessor Sharff.v. ir. th<» r'vrfonasdia nf Anatomy, &c. 



