Development, and Structure of the Vegetable Cell. 485 
is a layer of minute vesicles, which are rendered more evident 
by the action of a dilute solution of chloride of calcium. If a 
rather more concentrated solution of this salt be employed, the 
entire layer of vesicles, together with a delicate membrane by 
which it is enveloped, and which lines the somewhat thicker 
external cell-wall, is separated from the latter, which then ap- 
pears nearly smooth and structureless, or marked with small 
paler points, which appear to be the impressions of the vesicles 
previously closely applied to it (fig. 18). 
In a rather younger state, these vesicles are so small that no 
cavity is discernible within them. By endosmotic action, these 
vesicles, along with the cell-membrane surrounding them, be- 
come detached from the outer wall (figs. 10 & 11), which is 
then seen to be completely structureless and homogeneous. In 
somewhat older conditions, on the contrary, the membrane of 
the secondary cell, with the layer of vesicles adherent on its 
inner surface, are no longer separable by any such means from 
the mother cell, nor are the vesicles themselves expansible by 
_endosmotic action. These latter, indeed, appear in intimate 
union with the two superimposed cell-membranes, and exhibit 
themselves on the surface of the mother cell in the form of small 
warts or tubercles; and these again, in cells still more mature, 
assume the character of prickles, such as are seen distributed 
over the surface of the pollen-cells of Althea and of other Mal- 
vaceee (fig. 17). Simultaneously with this outgrowth of prickles, 
the collenchymatically thickened wall of the mother and primitive 
mother cells are absorbed. These, therefore, resemble in this 
respect the thickened membranes of the true collenchyma-cells, 
like which also they have the function of collecting nutriment 
for the younger endogenous cells. 
At the period when the tubercles first make their appearance 
on the surface, the membrane of the mother cell (originally the 
secondary cell) is coloured blue by iodine after contact for some 
time with chloride of calcium, but not at an earlier or later 
stage of growth. 
The existence of free daughter cells within the pollen mother 
cells, and the origin of septa by the coming into contact of their 
enlarging primary cell-membranes, are more readily observed 
in Monocotyledons than in the Malvacee, the mucilaginous 
juices of which render examination difficult. 
The pollen of Fuchsia is especially interesting, and the history 
of its development easily followed out. Moreover the nature 
of the interposed corpuscles, as I have stated in my essay on the 
Sexual Life of Plants (p. 25 e¢ seq.), can be made out in it, owing 
_ to frequent aberrations in structure under manifold forms. 
[To be continued. | 
