8 CONTENTS OF CELLS. 



state unite together directly, and become agglutinated, more or less, 

 according to their places of contact. Others, as Mohl and Henfrey, 

 hold that there is an intercellular matter which acts as a sort of 

 cement, or Collmchyma {xoXKa, glutinous matter). In sear-weeds, the 

 cells, of which the entire plant is composed, are placed at a distance 

 from each other (fig. 29, a a), and the intervals are fiUed up by this 

 interceUular substance (fig. 29, h), which thus forms a large part of 

 their bulk. In the higher classes of plants, when the cells touch 

 each other, the layer of intercellular matter must be very thm, except 

 in the interceUular canals or spaces. Mirbel looks upon it as the 



Pig. 29. Pig. 30. 



remains of the mucilaginous fluid in which the cells were originally 

 developed, and which has become thickened to a greater or less de- 

 gree, as in the root of the Date (fig. 30), where aaa indicate the 

 cells, and hhh the interposed substance. 



2. — Contents of Cells. 



The external membrane of cells is composed of the unazotised 

 substance called Cellulose, and in their interior a mucilaginous matter 

 is contained, which undergoes changes in the progress of growth. 

 This mucilaginous matter is the Protoplasm (•yjairos, first, and TXatf/ia, 

 formative matter) of Mohl, the Cytdblastema {xvrog, a cell, and 

 ffXasTiyj^a, growth) of some authors. It is at first homogeneous, but 

 ultimately assumes a granular form. The appearance of granules may be 

 regarded as the earKest evidence of the formative process. Protoplasm 

 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 primordial 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 thickening has advanced, this utricle dis- 

 appears, in consequence of becoming incorporated with the cell- wall. 



Fig. 29. CeUular tissue of Sea-weed {EvmaMhalia lorea). a a, Cells. 6, Intercellular 

 matter. Fig. 80. Central portion of young root of Date, aaa, Thickened cells. 6 6 ft, 

 ntercellular substance of Mirbel. 



