xii DEVELOPMENT OF THE TEXTURES. 



certain points, whilst they retire from each other elsewhere, so as to leave 

 radiating branches connected with the points of similar rays from adjacent 

 cells (fig. in.). 



3. The cells coalesce with adjoining cells, and open into them. In this 

 way a series of elongated cells placed end to end may open into one another 

 by absorption of their cohering membranes, and give rise to a tubular 

 vessel. 



4. Changes take place in the substance and in the contents of the cells. 

 These changes may be chemical, as in the conversion of starch into gum, 

 sugar, and jelly, and in the production of various coloured matters, essential 

 oils, and the like. Or they may affect the form and arrangement of the 

 contained substances ; thus, the contents of the cell very frequently assume 

 the form of granules, or spherules, of various sizes ; at other times the con- 

 tained matter, suffering at the same time a change in its chemical nature 

 and in consistency, is deposited on the inner surface of the cell- wall, so as 

 to thicken and strengthen it. Such " secondary deposits," as they are 

 termed by botanists, usually occur in successive strata, and the deposition 

 may go on till the cavity of the cell is nearly or completely filled up (fig. iv.). 

 It is in this way that the woody fibre and other hard tissues of the plant 

 are formed. It farther appears that the particles of each layer are disposed 

 in lines, running spirally round the cell. In place of forming a continuous 

 layer, these secondary deposits may leave little spots of the cell-wall un- 

 covered, or less thickly covered, and thus give rise to what is named pitted 



tissue (fig. ii., 6 ) ; or they may assume the form of a 

 Fig. IV. slender fibre or band, single, double, or multiple, running 



in a spiral manner along the inside of the cavity, or 

 forming a series of separate rings or hoops, as in spiral 

 and annular vessels (fig. n., 7 ). New matter may be 

 absorbed or imbibed into the cells ; or a portion of 

 p their altered and elaborated contents may escape as a 

 SECTION OP LI~GNEOUS secretion, either by transudation through the cell-wall, 

 CELLS CONTAINING or by rupture or absorption of the membrane. Lastly, 

 STRATIFIED DEPOSIT, in certain circumstances, cells may be wholly or partially 

 removed by absorption of their substance. 



5. Cells may produce or generate new cells. The mode in which this 

 takes place will be immediately considered, in speaking of the origin of 

 animal cells. 



FORMATION OF THE ANIMAL TEXTURES. 



Passing now to the development of the animal tissues, it may first be 

 remarked generally, that in some instances the process exhibits an obvious 

 analogy with that which takes place in vegetables ; for certain of the animal 

 tissues, in their earlier conditions, appear in form of a congeries of cells, 

 almost entirely resembling the vegetable cells, and, in their subsequent 

 transformations, pass through a series of changes in many respects parallel 

 to some of those which occur in the progress of vegetable development. 

 Cartilage affords a good example of this. Figures v. and vi., A, are 

 magnified representations of cartilage in its early condition ; arid whoever 

 compares them with the appearance of vegetable cells, shown in figures I. and 

 ii., must at once be struck with the resemblance. Fig. VT., B and c, shows 

 the subsequent changes on the primary cells of cartilage ; the parietes are 

 seen to have become thickened by deposit of fresh material, and the mass 



