COMPARED WITH THOSE OF ANIMALS. 51 



CHAPTER II. 



ON THE DEVELOPMENT AND PROPAGATION OF CELLS. 



So far as we at present know, the cell like the plant, is 

 the product of a previously existing cell. The principle 

 omne vivum ex ovo is applicable to vegetable matter under 

 whatever form it may present itself. Life is only known 

 as it is manifested through the agency of cells, and the 

 life-force appears to be generated in proportion to the 

 extent of their eombination and the development of their 

 functions. But how do the cells of plants and animals 

 orginate ? Whence come those new utricles which without 

 ceasing are added to those already in existence, and which 

 augment incessantly the mass from whence they draw their 

 origin ? These are difficult but exceedingly interesting 

 questions. '' 



There appear to be three principal modes in which cells 

 are multiplied, viz., by nuclei, by division, and by gem- 

 mation. 



1. FORMATION OF CELLS FROM NUCLEI. 



According to Schleiden, " cells can only be formed in 

 a fluid which contains sugar, dextrine, and proteine com- 

 pounds." They originate from a nucleus or cytoblast 

 (xv-foi a cell, and (BAaofoj a germ), which forms either in 

 the fluid when contained in the cavity of a pre-existing 

 cell, or in the midst of it when effused around the tissues 

 of growing parts. This fluid, — to which the terms cam- 

 bium, vegetable mucilage, and protoplasm have been ap- 



