CHAPTEE III. 



ON THE DEVELOPMENT AND FUNCTIONS OP CELLS. 



38. As all tlie parts of plants are fabricated out of cells, 

 it follows that growth, or the extension of their parts, is the 

 result of the development of new cells, and that the size and 

 form which plants assume must be owing to the number and 

 nature of the arrangement of the cells thus deyeloped. All 

 the varieties in the size, form, and duration of plants are, 

 therefore, simply the result of different degrees of cell- 

 evolution, and the same plan and principle of structure per- 

 vade the whole of them. To show that this is really the 

 case is the object of the present chapter. 



39. In all plants which consist of more than one cell, or 

 of a series of cells united together, a distinction must be 

 made between Vegetative cells, or those which aid in nutrition 

 and growth, and Reproductive cells, or those which continue 

 the species. All such plants continue to grow or extend in a 

 given direction so long as their vegetative cells continue to 

 develop ; but when the reproductive cells make their appear- 

 ance, the growth or extension of their parts in that direction 

 ceases. Now the endless variety of form and size amongst 

 plants is owing to peculiar modifications in their common 

 organs of vegetation and reproduction. Each species of 

 plant appears to be governed by peculiar organic laws, which 



