CHAPTER II 



THE PLANT-BODY 



SOME of the simplest organisms, like Amoeba (Fig. 2), and the 

 Slime-moulds or Myxomycetes, consist of naked, highly contractile 

 protoplasm, which in the latter contain many nuclei. Usually the 



protoplasm is segregated into 

 definite masses or cells, each with 

 a single nucleus, and in plants, 

 surrounded by a membrane or cell- 

 wall of cellulose. The cell-wall is 

 not an essential part of the cell, 

 and can be reproduced through the 

 activity of the protoplasm. Such 

 a large multinucleate mass of 

 protoplasm as the plasmodium of 

 the Slime-moulds cannot properly 

 be considered a single cell, and 

 this may be said of the large 



FIG. 2. Amoeba proteus, an organism 

 consisting of a naked protoplast; 

 n, nucleus; v, contractile vacuole; 

 /, food-vacuole containing a Diatom 

 (X200). 



" cells " or Coenocy tes of such 

 plants, as the Siphoneae ; e.g. Botry- 

 dium. The name " Energid " has been proposed for the structural unit 

 of organisms, an energid being defined as a single nucleus with the 

 surrounding cytoplasm which is under its influence. A plasmodium 

 of a Slime-mould, or the multinucleate cell of Cladophora, would 

 then represent an aggregate of -as many energids as there are nuclei. 



The Plant-cell 



The typical vegetable cell consists of a cellulose membrane enclos- 

 ing the cytoplasm or cell-plasm, in which is embedded the nucleus 

 and one or more green bodies, the chromatophores or chloroplasts. 

 Many of the lower plants consist of a single such cell, which exhibits 

 all the functions characteristic of the higher plant-forms. Such a 

 green cell represents the simplest form of a typical plant, and it 

 performs all the essential functions found in the highest plants. 

 It absorbs through the permeable cell-wall water containing in solu- 

 tion various inorganic salts ; and from the air, or dissolved in water, 

 oxygen and carbon-dioxide. Through the energy derived from light, 



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