28 THE ELEMENTARY STRUCTURE OF PLANTS. 



matter (11, vegetable mucilage, protoplasm, &c.) assimilated in 

 previously existing cells, and dissolved in the water which the tis- 

 sue of growing parts contains.* This organizable material always 

 and necessarily consists of a mixture of two classes of assimilated 

 matter, one of which is azotized, the other is not. That is, one is 

 composed of three elements, carbon, hydrogen, and oxygen, and 

 exists in the liquid form in the state of vegetable mucilage, dex- 

 trine, sugar, &c., or collects in a peculiar solid form in the cells, 

 as starch, or finally constitutes the proper and permanent wall of 

 the cell, under the name of CELLULOSE. The other is composed of 

 nitrogen in addition to these three elements, and exists in growing 

 parts in solution, as some state of \vhat is called proteine, and is 

 known among vegetable products in the forms of diastase, albumen, 

 gluten, fibrine, &c. The latter makes no portion of the per- 

 manent fabric, indeed ; but it plays an indispensable part in the 

 production of cells, and always exists in young and vitally active 

 cells, as a mucilaginous lining. A weak solution of iodine causes 

 it to turn brown, and detaches it from the proper wall of the celf. 

 According to Mohl, it appears earlier than the proper cell-wall, 

 which is formed under its influence, and is, as it were, moulded 

 upon it. Mohl has therefore given the appropriate name of pro- 

 toplasm to this azotized mucilaginous matter. 



28. From a Nucleus or Cyto'blast. When new cells are pro- 

 duced by original formation within the cavity of a parent cell, the 

 following processes appear to take place. Portions of " the proto- 

 plasm collect into a more or less perfectly spherical body, at length 

 sharply denned, the nucleus of the cell (Cyto'blast) ; upon this is 

 deposited a layer of protoplasm, which expands as a vesicle, and 

 forms the subsequent lining of the cell ; at a very early period the 

 whole becomes inclosed by a wall of cellulose, and the cell is com- 

 pleted." t This plan, under a more restricted form, was pro- 

 pounded, and until recently maintained, by Schleiden as the uni- 

 versal mode of cell-development. It is now maintained as one 

 principal mode only, and in a form essentially agreeing with 



* " Cells can be formed only in a fluid which contains sugar, dextrine, and 

 proteine compounds." Schleiden, I. c. 



t Schleiden, I. c., ed. 3 ; from the Appendix to the English translation. 

 " This appears to occur especially in the embryo-sac and the embryonal vesi- 

 cle." 



