in the Interior of Cells. 9 



a denser fluid present in large quantity and occupying the outer 

 parts of the cell-cavity, as has been already shown by other ob- 

 servers*. 



I dare not venture to express the slightest suspicion as to the 

 cause of this motion. It might be thought that the nucleus acts 

 an important part in it, forming as it does in most cases the 

 centre of the current, which might lead us to suspect that the 

 force producing it may have its principal seat in the nucleus, as 

 in Chara it cannot be denied that the chlorophylle granules 

 situated adjacent to the cell- wall have an influence on the cir- 

 culation of the sap. It appears to me however not probable that 

 the nucleus possesses any such influence. In the first place, it 

 is in many cases in the act of being dissolved precisely at the 

 time when the current is most rapid, at least it is smaller than 

 previously, for instance in the filamentary hairs of Tradescantia ; 

 on the other hand, the nucleus does not form the centre of the 

 current in Vallisneria in those cells in which the circulation is 

 very regular and rapid, but, like the isolated granules of chlo- 

 rophylle, follows the current without any quickening of the 

 movement being perceptible in its neighbourhood, or any other 

 circumstance tending to show that it had any special function. 

 It is true, I do not recollect having seen such currents in cells in 

 which the nucleus is already perfectly re-absorbed ; but this co- 

 existence of the nucleus and current may be accidental, and may 

 be explained from the protoplasma which forms the current being 

 re-absorbed earlier than the nucleus after the development of 

 the cell-walls. 



It is remarkable that the nucleus, considering its central posi- 

 tion, can be kept in its position in the cavity of the cell, not by 

 solid fibres, but by currents of a fluid, even though tenacious. 

 The observations above described respecting the changes in the 

 position of the nucleus destroy all idea of these currents, and 

 with them the nucleus, possessing a support in fibrous or mem- 

 branous tissues. We must therefore admit that the proto- 

 plasma, notwithstanding its motion, still has sufficient viscosity 

 to retain floating in the aqueous sap of the cell so small a 

 body as the nucleus. The older the cell becomes the more 

 does the substance of the current appear to harden, so that in 

 some cases at least it loses all its liquid and the currents be- 

 come solid filaments. I noticed this appearance most strikingly 

 in the flesh of the fruit of Rhamnus frangula, in which there are 

 some cells which arc far larger than the surrounding, and in 

 which is situated a nucleus fixed to filaments. These filaments 



* Schlciden, Grand zuge, 2nd edit., p. 292, and Hassall, British Freshwater 

 Algae, i. p. 85. 



