12 



CELLULAR TISSUE. 



from of tissue is simple, and results from a puckering inwards of the cell-wall towards 



the centre. If an orange "be cut through, and the 

 contents partly removed, and the rind be then 

 pressed by two or three fingers and a thumb until 

 the projected portions approach the centre, we may 

 form a correct idea of this form of tissue. Some- 

 thing more, however, is necessary. 



Inter-cellular Spaces. When a number of 

 cells are pressed closely together, so closely even as 

 to cause them to assume the form of a many (say 

 twelve) sided figure, there will yet be spaces of 

 triangular shape at each corner, at which the walls 

 do not absolutely touch. These are termed inter, 

 cellular spaces, and are the larger by so much as the 

 Fig. 31. The fibrous structure of the -n t c i ose i v applied to each other. When 



fowl's eo-z-shell, almost exactly simu- UU11& " ., i j -T. 



lating the cells of the Boletus (Fig. 25). these inter-cellular spaces are placed one over the 



other for some distance, they constitute inter-cellular passages, 



and are very abundant in all aquatic plants. The relation which 



the inter-cellular spaces bear to the stellate cells is this, that 



when the cell-wall is pressed inwards, in various direc- 

 tions, towards the centre 

 of the cell, the cell seems 

 to be reduced to a series 

 of arms (Fig. 30), whilst 

 the spaces between the 

 cells now appear to be a 

 series of cells themselves 

 (Fig. 32). These enlarged 

 inter-cellular spaces are 

 termed lacunce. 



The uses of the inter- 

 cellular spaces and pas- 

 sages are of great importance, since, in aqua- 

 of an aquatic tic P lants ("* wnicl1 &ey chiefly abound), they 

 contain the air which imparts buoyancy, and re- 

 tains' it on the surface. This fact may, in some 

 degree, account for the great size of these spaces in many aquatic plants (Fig. 33). 

 In other plants, their use is chiefly that of a depository of secretions. 



ing the formation of in- 

 ter-cellular spaces in 

 disease. 



Fig. 33. Air-chambers 

 plant the LIMNOCHAIUS PLUMIERI, ex- 

 kibiting_extreme regularity of form. 



Before concluding our account of cells we must briefly refer to some modifications. 



The DOTTED CELL differs from the ordinary cell only in having been constructed from 

 dotted membrane in place of plain. This form is very abundant, and especially in the 

 stem of the vine (Fig. 13) and other fast-growing plants, in the bark of most wooded 

 trees, and in the roots of many plants, as of the common horse-radish. They are 

 usually of large size. 



Thick-walled Cells, or Sclexogen, are the result of the deposit of the 

 peculiarly hard tissue termed sclerogen, on the inner side of the cell-wall. This 

 substance is usually found deposited in concentric layers (Fig. 34), so that at length 



