THE VEGETABLE CELL 



287 



A different view of the composition of the cell- wall has been 

 advanced in recent years by ^\'iesner. He holds that the sub- 

 stance of cell-wall as it is first formed consists of rows of 

 granular bodies which he terms dermatosomcs, which are united 

 together and surrounded by protoplasm. On this hypothesis the 

 cell-wall is living while young and growing. The protoplasm 



Fig. 616. Fig. 617. 



Fig. 618. 



Fig. 619. 



Ftcr. 616. Eouaded cells. Fuj.iU. Elliptic or oblong cell. «5fs.618, 619. 



Polygonal cells in combination : those of the latter figure being pitted. 



thus exists between particles of cellulose, and holds water in its 

 substance. 



As the cells grow there is a continuous formation of cellulose, 

 due, like its first formation, to the vital activity of the protoplasm. 

 By irregularity of growth, due to internal causes bringing about 

 greater possibility of stretching in certain places, cells become of 

 various forms ; when the growth is uniform, or nearly so, in all 

 parts of the cell- wall, we have a spherical or rounded cell (fig.- 

 616) ; but when it is greater at the two extremities than at the 

 sides, the form is oval or oblong [fig. 617). In the above cases, 

 also, the cells are almost, or entirely, free from external pres- 

 sure. But, under other cir- 



FlG. 620. 



Fig. 621. 



cumstanoes, m consequence 

 of the mutual pressure of 

 surrounding cells, they as- 

 sume a polygonal form (figs. 

 618 and 619), the number of 

 the angles depending upon 

 the mimber and arrangement 

 of the contiguous cells. 



When the growth is nearly 

 uniform on all sides of the cell- 

 wall, but not equally so at all 

 points of its surface, we have 



cells which maintain a rounded form in the centre, but have 

 rays projecting from them in various directions, by which they 



<3 



I'i.j. 620. Stellate cells. «,/. 621. Cylin- 

 drical cells. The small rounded body in 

 the interior of three of these cells is the 

 nucleus. 



