99 



Secondly. That all the cells have an extremely thin lining, the 

 slightest wound of which is death to that cell. This lining is in 

 most cases regularly paved with vesicles, the colour of which deter- 

 mines the colour of that portion of the plant. These appear to 

 regulate the circulation; for when any accident damages or re- 

 moves them near the boundary between the to-and-fro currents, some 

 of the fluid will anastomose, i. e., will pass the boundary and 

 return as shown by the arrows, in fig. 23, instead of continuing 

 its course to the end and there returning. 



The specimen from which this was drawn had been injured ; it be- 

 came healed within a fortnight, new vesicles grew, and again covered 

 the place of the wound, the circulation then became regular, none 

 going over the boundary. The place appeared fresh, the new studs 

 being paler and rather smaller than the old ones. 



Thirdly. That there are two fluids in each cell that do not inter- 

 mingle. The central fluid is passive, and thinner than the circulating 

 one, which it supports against the lining, and to which it seems to 

 adhere and along which it appears to slide, dragging the central fluid 

 with it. This I believe to be a law of vegetable circulation. 



Fourthly. That gravity affects the visible masses of matter in the 

 central passive fluid, but not in the circulating fluid. In whatever po- 

 sition the plant may be placed, circulation will go on well. But let 

 the plant be put horizontally, as in fig. 24, with the side that has large 

 masses uppermost, these will fall to the lower side and return with 

 that current; again change the position, they will fall back into the 

 first current, and be carried along with it. This proves that there is 

 no partition between the two currents ; accordingly, when a mass 

 happens to be in the centre, it only revolves without changing its 

 place, as shown in fig. 25. This fact may be most frequently seen 

 in Nitella translucens, from its being four times as thick, and always 

 without the covering of carbonate of lime. At the bottom of the 

 figure globules have accumulated in sufficient number to obstruct 

 each other's rising. 



FiftJdy. That the cells of the plant are of four kinds, each possess- 

 ing separate qualities. 



1. Those of early maturity. 



2. Cells with green vesicles in motion, and no fixed ones. 



3. Cells that have a flexible mass sliding round in the circulating 

 fluid. 



4. Cells with no extra feature in the fluid. 



