CONTENTS OF CELLS. 



This matter is the Protoplasm (K^UTO;, first, and ^-Aa^a, formative 

 matter) of Mohl, the Cytoblastema (XVTOJ, a cell, and /SAaar^a, a germ) 

 of some authors. It is at first homogeneous, but ultimately assumes 

 a granular form. It contains nitrogen in its composition, or is azotised, 

 and it assumes a brownish colour when acted upon by iodine. It 

 forms a mucilaginous layer on the inner surface of the cell-wall, and 

 thus gives rise to the internal utricle of Harting and Mulder, the prim- 

 ordial utricle of Mirbel. This inner membrane is visible in the young 

 state of the cell, and under the action of tincture of iodine may be 

 made to contract and separate from the outer cell-wall. It may also 

 be rendered distinct by the action of strong hydrochloric acid, and by 

 diluted sulphuric acid. When the process of lignification or thicken- 

 ing has advanced, this utricle disappears, in consequence of becoming 

 incorporated with the cell-wall. 



15. In certain cells the membrane continues throughout to be formed 

 of a thin layer of cellulose, while in others it becomes thickened by the 

 deposition of matter on its inner side. These secondary deposits, or in- 

 crustations, are sometimes of a gelatinous consistence; at other times they 

 are hard. In the latter case, the incrusting matter is looked upon as a 

 modification of cellulose, and has received the name of li<jnine (lignum, 

 wood), or sclerogen (o-xXfoV, hard, and ytwu.tiv, to generate). On mak- 

 ing sections of such cells, in a transverse (fig. 31) or longitudinal di- 

 rection (fig. 32), the successive layers may 



be seen either continuous all round, or leav- 

 ing parts of the membrane uncovered. Cells 

 of this kind are well seen under the micro- 

 scope in thin sections of the hard shell of the 

 Coco-nut, or of Attalea funifera, and of the 

 hard seed of the Ivory Palm. In all cell- 

 deposits there is a tendency to a spiral ar- si 

 rangement. When the deposition is uniform over the whole surface, 

 this arrangement may not be detected ; but when interruptions take 

 place, then the continued coil becomes evident. In spiral cells the 

 fibre seems to be formed before the full development of the cell, the coils 

 of the fibre being at first in contact, and afterwards 

 separated, whereas the secondary thickening layers are 

 deposited after the cell is fully formed. 



16. Each cell is found to contain, at some period of \__// j-j 0; 

 its existence, a small body, called a nucleus (fig. 33 nn ri), 



in which there are often one or two, rarely more, min- 

 ute spots, called nucleoli. The nucleus is of a round 

 or oval shape, granular and dark, or homogeneous 

 and transparent, bearing some resemblance to a smaller internal cell. 



Fig. 31. Transverse section of cells from pulp of Pear. 



Fig. 32. Longitudinal section of the same. Fig. 33. Nucleated cells from the Beet. 



