THE CELL-WALL. 485 



chyma-cells of Orchis, CucurUta, &c. with sulphuric acid, where the 

 appearance often results from the irregular convolutions of the swollen 

 lamellaa of the cell- wall. 



Fig. 531 B. 

 Fig. 531 A. 



Pig. 531 A. Section of cells of the endosperm of a Sago- Palm. Magn. 200 diam. 

 Fig. 531 B. Laminated cell- walls of the cells in A. Magn. 500 diam. 



The uniform kind of secondary layers are sometimes accumulated 

 at one side (fig. 534), or in the angles of cells (fig. 535) : thus 

 they are much thicker on the side of epidermal cells next the air ; 

 and they fill up the angles of the cells of the fleshy endosperm of 

 many seeds, the cells of the collenchyma found beneath the rind of 

 Chenopodiacese, and the cells of the leaves of Nymplicea, of some 

 Jungermanniacese, &c. There is reason to believe that, in some 

 instances, the cell-wall thickens at certain seasons and becomes 

 thinner at others ; but this appearance may arise from an alter- 

 nately swollen and contracted state, and not from absorption and 

 redeposition. 



The subject will be alluded to again under the heads of epidermis and 

 intercellular substance. 



Pitted Cells. The deposits which leave spots of the primary 

 membrane bare form what are called pitted, or, less properly, porous 

 cells. They occur on the walls of most cells of the parenchyma- 

 tous structures of the higher plants, in the form of round spots 

 (fig. 526), where the still membranous cell-wall is thinner. In 

 wood-cells, in liber-cells, and the greatly thickened cells of fleshy 

 endosperms, hard seed-coats, &c., the formation of a great num- 

 ber of secondary layers upon the wall, always leaving those spots 

 bare, converts the pits into canals running out from the contracted 

 cavity to the primary wall (figs. 530, 531). 



The marks are really always pits at first, as may be seen by colouring 

 the cell-membrane with iodine. But in old wood-cells they appear some- 



