CHAPTER III 



CELL COMMUNITIES: A CHAPTER ON TISSUES 



Cell joined to cell, mysterious Life passed on 

 By viscous threads ; selecting in its course, 

 From formless matter, with mysterious touch 

 That seems a prescience, and that never errs, 

 Materials diverse, out of which to weave 

 The warp and woof of tissues. 



in VERY plant, as already mentioned, consists either of a cell or cells, or 

 JDj of the products of their formation and transformation. When a 

 Rose-tree begins to grow, its growth is not effected merely nor chiefly by 

 the increase in size of already existing cells, but by the formation of cells 

 entirely new ; and this is true of all multicellular plants. Of course, cell 

 multiplication (as it is called) also takes place in unicellular plants. This we 

 saw to be the case with Sphcerella pluvialis ; but 

 in such instances the new cells become distinct 

 individuals ; they cease to form part of the 

 parent plant, and enter upon an entirely inde- 

 pendent existence. 



Now, cells may multiply in four ways. Free 

 cell formation is one of these ; and we take this 

 mode of increase first, because it is the means 

 by which both the resting and zoospores of 

 Sphcerella are produced. The pollen-grains of 

 most Flowering Plants are formed in this way, 

 as well as many zoospores besides those of 

 Sphcerella. The process has been already de- 

 scribed at some length, and there is no need to 

 go over the ground again. 



Sometimes, however, the entire protoplasm 

 of the parent cell, instead of dividing off into 

 several individuals, is used up in the formation 

 of a single new cell. This mode of cell forma- 

 tion, which is like a renewing of the youth of 

 the individual, is appropriately termed rejuven- 

 escence. 



73 



FlG. 102. SlLKWEED OR 



CROW-SILK. 



Portions of the filaments of six separate 



plants. In the second three filaments ten 



of the cells are seen to be in various 



stages of conjugation. 



