32 



PLANT LIFE. 



seacoasts, is not divided into nodes and internodes, and the 

 branches are differently arranged from those of Chara. The 

 ^ axis is made up in its larger parts of five or 



more rows of cells, the central or axial row 

 being surrounded by a jacket of at least four 

 > others (fig. 40). But these originate by 

 f i division from the central one, and are not, as 

 ' $ in Chara, merely adherent to it. It is, how- 

 Yf ever, only in the larger parts of the axis that 



Fig 



Fig. 39.— An entire plant of Polysiphonia, showing mode of branching. Natural 



size. — After Kutzing. (See fig. 229.) 

 Fig. 40. — Transverse section of one of the branches of Polysiphonia, showing a 



minute central cell with four large and four small cells surrounding it. Magnified 



about 50 diam. — From a drawing by Mr. Grant Smith. 

 Fig. 41. — Apex of a branch of Polysiphonia which has nearly ceased growing. 



Magnified about 100 diam. — From a drawing by Miss Rowan. 



this structure appears ; at the tips even of the main axis the 

 body is a linear aggregate (fig. 41). Polysiphonia, there- 

 fore, may be looked upon as one of the simplest forms of a 

 solid aggregate. 



39. Apical cell. — As in Chara, growth in length is quite 

 definitely localized, because it is the elongated terminal cell 

 of either the main or secondary axes (fig. 41) which pro- 

 duces, by division near its base, the new cells whose subse- 

 quent enlargement and division give rise to the axis. In 

 some red algae the chambers are not cells but ccenocytes, as 

 shown by the several nuclei. 



40. Color. — -In this plant, as in very many of the marine 



