CHAPTER VIII 



THE PLANT BODY 



The evidence seems to show beyond question that our present 

 species of plants have descended by gradual evolution from 

 simpler and fewer species which formerly existed back, it 

 is possible, to a single kind which throve in remotest antiquity. 

 Ganong. 



NEARLY all stages exist between the simplest unicellular 

 plant body such as is exhibited by Sphaerella, and the highly 

 complex condition which obtains in the familiar FLOWERING 

 PLANTS, technically known as SEED PLANTS or SPERMA- 

 TOPHYTES. A simple type is found among the filamentous 

 green Algae commonly called pond scums. In forms such as 



>*" -"--, 



FIG. 22. Spirogyra. Portion of a filament, highly magnified, showing cell wall, 

 cytoplasm, nucleus, vacuole of cell sap, and spiral chloroplastid. (From Coulter.) 



Spirogyra the body of the plant consists of a series of similar 

 cells placed end to end and, therefore, from one point of view, 

 may be looked upon as a colony of cells since the individual 

 cells of the filament are essentially independent. (Fig. 22.) 

 In Ulothrix, another simple form, the filament instead of 

 floating free is attached by a more or less specialized cell 

 devoid of chlorophyll. (Fig. 49, A.) Still more common 

 are plant bodies composed of branching filaments of cells. 

 The branches may all be similar, or there may be a chief axis 



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