FORMATION AND GROWTH OF CELLS. 27 



and has the same composition (when pure) in all plants. This sub- 

 stance — the general material of vegetable fabric — is called Cellu- 

 lose. Its chemical composition is Carbon 12, Hydrogen 10, and 

 Oxygen 10. It is insoluble in water, alcohol, ether, and dilute acids, 

 and, like starch, it turns blue when acted upon by iodine, aided by 

 sulphuric acid. The primordial utricle, or delicate lining of the 

 cell, appears to have the same composition as protoplasm. It may 

 be regarded as an exterior portion of the mucilaginous protoplasm, 

 which has acquired the consistence of a very soft membrane. In 

 addition to the three elements, carbon, hydrogen, and oxygen, pro- 

 toplasm contains nitrogen, in considerable quantity. It is colored 

 yellow by iodine, and is coagulated by alcohol* and acid*. The 

 substance of which it principally consists is named by chemists 

 Proteine, and is known among vegetable products under various 

 forms, viz. as diastase, gluten, fibrine, vegetable albumen, and the 

 like. Such being the nature and the parts of the cell, we may now 

 consider 



28. Its Formation and Growth. Under this head we may briefly 

 explain, as far as we are able, — 1st, how cells are originated; and 

 2d, how they are multiplied. 



29. Original Cell-Formation. Cells are originated only within other 

 cells, or at least in matter which has been contained in and elab- 

 orated by them. They appear to be formed in the following man- 

 ner. A portion of the elaborated or organizable matter, which 

 abounds in the fluid contents of living cells, condenses into a soft 

 solid, or half-solid and more or less transparent mass, usually of a 

 globular or oval shape, the nucleus : around this nucleus a portion of 

 protoplasm accumulates ; a denser film of the same substance forms 

 on the surface of the protoplasm, giving the mass a definite outline ; 

 this is the primordial utricle : upon this a layer of cellulose is soon 

 deposited, making the cell-membrane. The nuclei in such cases are 

 very minute, and either few or many of them may be formed in 

 one parent cell, and be developed in this way into new cells, which 

 are, at least at first, of small size as compared with the parent cell 

 (Fig. 88). A variation of this mode occurs in many of the lower 

 Algae, where a considerable portion of the contents of a cell con- 

 denses into a rounded mass, the surface becomes coated with a 

 layer of protoplasm or primordial utricle, and this with a membrane 

 of cellulo e, completing the cell. Thus, in Vaucheria the whole 

 green contents at the end of certain branches condense into a 



