THE CELL AS A MEMBER OF A GROUP. 33 



CHAPTER VI. 



THE VEGETABLE CELL AS A MEMBER OF A GROUP. 



1. ONLY a comparatively small number of plants 

 consist of a single cell. These are the simplest forms 

 of plant life. In the greater number of vegetables 

 the cells are united into groups. Cell-families may 

 originate from a single mother-cell, and remain for a 

 time closely connected, or contiguous, yet each 

 daughter-cell preserves its own individuality, and 

 may originate a new colony. Such cell-families only 

 occur in the lowest classes of plants. In the higher 

 classes the union of cells which forms tissues and or- 

 gans is permanent, and the separate cells are often so 

 closely united as to form a single cavity or vessel ; 

 the cell-walls of young contiguous cells fusing into a 

 common mass, or cells originally distinct uniting in 

 those parts of the walls which are in contact. This 

 union is so strong as only to be destroyed by chemical 

 agents which dissolve the cell-wall. Yet sometimes 

 cells which have partially united separate from each 

 other, forming a cavity. These spaces also may be 

 grouped together so as to form passages, or air-canals. 



2. The woody fibers of plants, and the cellular 

 tissue which makes the softer, fleshy, and pithy parts, 



