568 APPENDIX. 



Page 31., substitute for 14. 



14. By the plant-cell (cellula) I understand exclusively the 

 elementary organ, which, when fully developed, possesses a wall 

 formed of cellulose and a semi-fluid nitrogenous lining, constitut- 

 ing the sole essential element of form of all plants, and without 

 possessing which nothing can be called a plant (ohne ivelche eine 

 Pflanze nicht bestehf). 



Cells can only be formed in a fluid which contains sugar, dex- 

 trine, and proteine compounds (formative matter, cytoblastema). 

 The proteine compounds appear to be the primary producers of 

 the process here, as in the chemical metamorphoses ( 11.). Two 

 points must be distinguished : 



I. The formation of cells without the influence of another cell 

 previously existing. This occurs in fluids capable of fermentation. 

 A globule of nitrogenous substance originates ; in this a cavity is 

 formed, it grows, and the complete cell has a delicate coat of cellu- 

 lose, without our being able to determine the epoch of its pro- 

 duction. 



II. Formation of cells under the influence of a complete cell 

 already existing, or multiplication of the plant-cell. The mode of 

 multiplication of vegetable cells does not appear to follow the same 

 type in all cases. Apparently we may at present distinguish at 

 least two kinds of multiplication. 



1. The nitrogenous substance, the protoplasma, collects into a 

 more or less perfectly spherical body, at length sharply defined, 

 the nucleus of the cell (cytoblastus) ; upon this is deposited a layer 

 of protoplasm, which expands as a vesicle, and forms the subse- 

 quent lining of the cell : at a very early period the whole becomes 

 enclosed by a wall of cellulose, and the cell is completed. This 

 appears to occur especially in the embryo-sac and the embryonal 

 vesicle. 



2. The whole contents of a cell, including the nitrogenous 

 lining, divide into two portions, which appear to be separated by 

 a lighter zone ; and around each portion is formed a wall of cellu- 

 lose. The nucleus of the cell appears to behave differently here, 

 since : 



a. It divides, and is thus doubled, so that each of the newly- 

 formed nuclei becomes the central point for one of the cell-forming 

 portions of the contents ; or, 



b. It disappears, so that a new nucleus is developed in each of 

 the new cells after their production. 



This mode (2.) of multiplication appears to occur in all the 

 other parts of the plant. 



This subject requires a very great deal more investigation. 



I exclude from the term "cell" all hollow elementary particles of 

 plants which do not bear the characters given in the paragraphs ; and 



