8 
Wenham, on the Vegetable Cell. 
a thin membrane is next formed, which constitutes the end 
wall of the two cells. The two membranes gradually approxi- 
mate towards each other, and the intervening protoplasm 
disappears. 
In instances where the cell is of excessive length, a larger 
mass of protoplasm accumulates midway, in the centre of 
which a cavity makes its appearance, as at a, fig. 10 ; this 
enlarges, and becomes lined with a membrane, and thus di- 
vides the original cell space into three parts. 
A tissue of cells, in the stage of development represented 
by fig. 9 is nearly colourless ; it is about this period that it 
begins to emerge out of its dark location, so far as to give the 
first indications of the chemical action of light in causing the 
deposit of chlorophyll instead of starch. The minute granules 
of starch, previously scattered throughout the cells, serve for 
the nuclei of the chlorophyll granules. At first they are enve- 
loped in a delicate green coating, which becomes thicker, and 
more decided in colour, as the cell approaches further into the 
light. These incipient chlorophyll granules are now frequently 
carried about in the currents of protoplasm circulating in the 
cells at this time. A single atom of starch is suflicient for 
the nucleus of a chlorophyll granule, but sometimes the green 
coating is deposited simultaneously upon a group of several 
together. 
Fig. 11 represents the cells of a \e?ii oi Anacharis in its 
latest stage of vital existence. The cell walls having now 
attained their utmost degree of thinness and consistency, the 
entire leaf acquires a yellow tinge, from the altered colour of 
the shrunken and partly dissolved chlorophyll granules (hence 
termed xanthophyir^, which now so far disappear, that some 
cells contain only two or three, much disintegrated. At this 
period the leaf cells, though apparently in their first stage of 
decay, are probably performing their most important functions, 
by afipording nutriment to the growing plant, by the dissolution 
of their contents. In the specimen here drawn a rapid cur- 
rent of protoplasm was traversing the interior of each cell. 
This motion is perhaps quite as necessary for the solution of 
the cell contents as for their formation by successive deposits ; 
in fact, the phenomena of cell circulation are oftentimes best 
seen at this stage. 
I have omitted to mention that indications of a strong en- 
dosmotic force are perceptible throughout the entire course of 
cell formation. The cavities spontaneously formed in an 
exuded mass of protoplasm sometimes burst from the accumu- 
lation of fluid in their interior ; many unicellular plants, after 
being partly dried, will also burst on being again subjected to 
