200 THE SECOND BOOK OF BOTANY. 



But the life of the cell is not in its membranous 

 wall, which is rather a skeleton, or framework, for 

 the support of the vital parts. 



That portion of the cell-contents which lies next 

 the cell-wall is a semi-fluid, turbid substance, always 

 present in young, growing cells, and such as are re- 

 producing other cells, or doing work of any kind. 

 The name of this substance is protoplasm, and it is 

 found wherever there is life. It is not a membrane, 

 but a mucilaginous substance, 

 FIG. sea. which moulds itself upon the cell- 



wall, is flexible, ductile, and not 

 unlike the condition of glass at 

 the instant the glass - blowers 

 mould it. In Fig. 363 is seen 

 the cell-wall (&), with its lining 

 of protoplasm (5). The round 

 body (c) in the interior is the nu- 

 cleus of the cell, within which the 

 nucleolus is also shown as a white spot. In young 

 cells the protoplasm and nucleus nearly fill the space, 

 but the cell-membrane is kept expanded by the sap. 

 Protoplasm does not dissolve in water, or even mix 

 with it. It has the power of contractility, and, in 

 living cells, is constantly in motion. When highly 

 magnified, it is found to contain a vast number of 

 minute granules, which circulate in streams, having 

 particular directions. This beautiful phenomenon of 

 circulation in cells is well seen in the jointed hairs 

 which cover the stamens of the Yirginian spiderwort. 

 It seems to result from a property, possessed by 

 all protoplasm, of constant motion in some form or 

 other. 



