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 

 division from the central one, and are not, as 

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

 ever, only in the larger parts of the axis that 



Fig. 39. 



Fig. 



Fig. 41. 



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



size. — After Kiitzing. {See tig. 229.) 

 Fig. 40. — Transverse section of one of the branches of Pc^lysi/'honia^ showing a 



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



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

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



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



this Structure a]5pears ; 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 localizetl, 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 alga; the chamljers arc not cells but ccenocytes, as 

 shown by the several nuclei. 



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



