CONTENTS OF CELLS. 



495 



Fig. 546. 



Protoplasm. In all 

 young growing cells we 

 meet with a tough muci- 

 laginous semifluid sub- 

 stance, colourless or with 

 a yellow tinge, and fre- 

 quently of more or less 

 granular character, which 

 increases with the age of 

 the cell. This substance 

 is called the protoplasm. 



The sperm or elementary 

 units (male) and the cor- 

 responding initial germs, or 

 female organs, are fragments 

 of naked protoplasm. The 



MvxomvcetOUR Funi aie Transverse section of cell of Junqermaunia Taylori: a, 



very remarkable. They ^SjS^X^Sf 1 ^^^^^^^^ 



consist of masses of proto- . 



plasm, called plasmodia, uncvered by cell-membrane, and which move 

 by creeping over the substance on which they grow, show currents in 

 their interior, and ultimately form reproductive bodies, covered with a 

 cell- wall formed from their 'own substance (see p. 470). Latterly Mr. 

 Francis Darwin has shown that protoplasmic filaments may be ejected 

 and retracted from the cells of the leaf of the common Teazel. 



Ecto- and Endoplasm. The protoplasm generally presents a division into 

 two layers the outer a hyaline film in contact with the cell- wall, and 

 called the ectoplasm, the other of a granular character, termed the endo- 

 plasm. The ectoplasm or primordial utricle is the outer film of the pro- 

 toplasm, from which it differs in its greater density and different mole- 

 cular structure. It may be seen by soaking the tissue in acetic acid, 

 is coloured yellow by iodine, and is applied intimately to the inner 

 surface of the cell-membrane of young cells, persisting in the cells of 

 tissues which are concerned in the reproduction of cells or the perfor- 

 mance of the functions of assimilation, &c., but disappearing at a com- 

 paratively early period in cells which acquire fibrous or pitted woody 

 secondary layers. 



The ectoplasm, lining the entire wall of the cell, forms a kind of sac ; but 

 it is not a membrane in the same sense as the proper cell-wall, since, 

 although it presents a certain cohesion and resistance to the penetration 

 of water, it is not merely flexible, but ductile, and capable of moulding 

 itself into new external forms, the sac, in cell-division, becoming con- 

 stricted into two or more portions without wrinkling. When the zoo- 

 spores of the Algae escape from the parent cell, the primordial utricle 

 forms the external boundary of the structure of the zoospore, which has a 

 definite form in each case. The ectoplasm presents a radial striation, 

 rendered more evident by the action of osmic acid. According to Stras- 

 burger it consists. of small rods of relatively dense substance, with the in- 

 tervening spaces filled with cell-sap or watery protoplasm. The cilia of 

 zoospores, which are extremely fine vibratile threads, are productions 



