44 PLANT LIFE 



the slippery gelatinous character of its mem- 

 branes. The cells of the filaments are com- 

 monly elongated, but each one behaves very 

 much as an independent unit. The effect of 

 one cell upon another is of the slightest under 

 ordinary circumstances. Each divides trans- 

 versely, and so multiplies, independently of 

 its neighbours. The filament thus grows in 

 length, but it usually has no distinguishable 

 base or apex, nor does it branch. Altogether 

 the organising effect of the cell union is as 

 yet of the very simplest kind. 



Another common alga, Cladophora, presents 

 quite a different state of affairs (Fig. 6). This 

 plant, like the foregoing, consists of cells placed 

 end to end, but there the similarity ceases. 

 Each cell is definitely part of the organism. 

 The filament is attached by a specialised basal 

 cell and it increases in length solely by trans- 

 verse division of the apical cell. Branches 

 may spring from the cells behind the apex, 

 and they then commonly appear in regular 

 sequence, the youngest branches arising as 

 outgrowths from the anterior (e. g. nearer the 

 growing point of the stem) end of the cell 

 nearest the apex. 



Not only, therefore, is the plant as a whole 

 organised in such a way that there is a base, 

 as distinct from an apex, but this distinction 

 is also impressed on every cell l which helps 



1 In a certain sense the expression " cell "' is not 

 appropriate to the structural unit of Cladophora, since 

 each " cell " really represents a syncytium (p. 21) because 

 its protoplasm contains several nuclei. 



