THALLOPilYTES : ALG^ 



plex plants consist of very many cells. It is necessary to 

 know something of the ordinary living plant cell before the 

 bodies of Algae or any other plant bodies can be under- 

 stood. 



Such a cell if free is approximately spherical in outline, 

 (Fig. 6), but if pressed upon by contiguous cells may become 

 variously modified in form 

 (Fig. 1). Bounding it there 

 is a thin, elastic wall, com- 

 posed of a substance called 

 cellulose. The cell wall, 

 therefore, forms a delicate 

 sac, which contains the liv- 

 ing substance known as^ro- 

 tojylasm. This is the sub- 

 stance which manifests life, 

 and is the only substance 

 in the plant which is alive. 

 It is the protoplasm which 

 has organized the cellulose 

 wall about itself, and which 

 does all the plant work. It 

 is a fluid substance which 

 varies much in its consistence, sometimes being a thin vis- 

 cous fluid, like the white of an egg, sometimes much more 

 dense and compactly organized. 



The protoplasm of the cell is organized into various 

 structures which are called organ>< of the cell, each organ 

 having one or more special functions. One of the most 

 conspicuous organs of the living cell is the single nucleus, a 

 comparatively compact and usually spherical protoplasmic 

 body, and generally centrally placed within the cell (Fig. 1). 

 All about the nucleus, and filling up the general ca^^ty 

 within the cell wall, is an organized mass of much thinner 

 protoplasm, known as cytoplasm. The cytoplasm seems to 

 form the general background or matrix of the cell, and the 



Fig. 1. Cells from a moss leaf, showiDg 

 nucleQS {B) in which there is a nucle- 

 olus, cytoplasm (C), and chloroplasts 

 (JL).— Caldwell. 



