CHAPTER XII. 



THE MAINTENANCE OF BODILY FORM. 



Every plant is capable of attaining and maintaining a 

 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, Botrydium ; B, Draf>arnaldia ; C, Coleochcete ; 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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