CHAPTER XII. 



THE MAINTENANCE OF BODILY FORM. 



EVERY plant is capable of attaining and maintaining n 

 specific form, which is not permanently altered by the direct 

 action of external forces, and is dependent upon the nature 

 of the plant itself. 



187. Naked cells. If the plant consists of a single mass 

 of naked protoplasm, it may assume a spherical or ovoid 

 shape (fig. 1 68). In attaining this form the physical forces 



FIG. 168. Zoospores of various forms, swimming in water by means of one or more 

 cilia. A, Botrydiunt ; B, Drafarnaldia ; C, Coleochtete ; D, CEdogonium. 

 Highly magnified. After Kerner. 



constituting surface tension play a part, but the form is deter- 

 mined chiefly by internal forces inherent in the protoplasm. 

 This is particularly well shown when such organisms extend 

 delicate protoplasmic threads, the cilia, and maintain these 



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