44 PLANT LIFE. 



dextrose, and dextrin, and in some instances from glycerin 

 mannite, etc. 



Plant Tissues. — Those combinations of cells that originate 

 from one common law of growth or cell-formation, and 

 that are from the first organically united, are called tissues, 

 as opposed to masses of cells that were originally independ- 

 ent becoming adherent, or to rows of cells becoming more 

 or less interwoven and exhibiting a common growth, as in 

 many fungi ; such combinations are known as spurious 

 tissues, ox pseudo-parenchyma. 



As already stated, a single cell may constitute an in- 

 dividual, many such unicellular or one-celled plants always 

 remain isolated, in others the daughter-cells produced by 

 the mother-cell remain in clusters of definite form, each 

 daughter-cell retaining its individuality. Such collections of 

 individuals are termed cell-colonies, and remain in mechanical 

 contact, usually held together by a mucilaginous substance 

 secreted by the members of the colony. Finally the in- 

 dividuals separate, each in turn being the mother-cell of a 

 new colony. In other examples the individuals of a cell- 

 colony are for some time organically united by strands of 

 protoplasm, eventually becoming free, and in a sense 

 forming a transition from cell-colonies to true tissues. 



The following are the most important aggregations of 

 cells to form tissues. 



Filaments consist of a single row of superposed cells in 

 contact by their contiguous ends only. Many of the simpler 

 species of algae consist of such unbranched cell-rows : the 

 same arrangement of cells occurs in the hairs of some 

 flowering plants. 



Cell-surfaces. — The cells combine to form a continuous 

 layer only one cell in thickness. Such membranaceous 



