CHAPTER XIII. 



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. 



155. Naked cells. — If the plant consists of a single mass 

 of naked protoplasm, it may assume a spherical or ovoid 

 shape (fig. 109). In attaining this form the physical forces 



Fig. 109. — Zoospores (naked pro.oplasm) of various kinds, swimming in water by means 

 of one or more cilia. A , Boirydium : 3, Draparnaldia ; C, ColeocktBte : D, 

 (Edogonium. Highly magnified.— After Kemer. 



play a part, but the form is determined chiefly by unknown 

 internal forces peculiar to living protoplasm. This is par- 

 ticularly well shown when such organisms extend delicate 

 protoplasmic threads, the cilia (fig. 109), and maintain these 



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