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 th6m. 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 Althcea and of other Mal- 

 vacese (fig. 17). Simultaneously with this outgrowth of prickles, 

 the coUenchymatically 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 Malvacese, 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 et seq.), can be made out in it, owing 

 to frequent aberrations in structure under manifold forms. 

 [To be continued.] 



