CELLTJLAE, TISSUE. 19 



parenchyma or green stratum of vegetable matter in the leaf, 

 where the cells are globular by mutual compression, they 

 assume an hexagonal or honey-comb like structure (Fig. 2). 



Fig. 2. 



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The form of the cells, therefore, depends entirely on the cir- 

 cumstances in which they are placed, varying greatly in dif- 

 ferent parts of the same plant, their form being modified by 

 the growth and peculiar functions exercised by the organs of 

 the plant. 



8. In the simpler tribes of plants, such as mosses and algae, 

 the cells depart but slightly from their primitive form, which 

 they retain throughout the entire life of the plant. But in 

 the more highly organized and complex plants, although the 

 mass of the plant at first consists wholly of cellular tissue, yet 

 as soon as the embryo plant begins to germinate, even whilst 

 the cotyledons or first pair of leaves are yet developing above 

 the earth's surface, certain cells are seen rapidly to depart 

 from their primitive form, and to assume an elongated or 

 tubular appearance ; the septa, or walls, or partitions between 



