CHLOROPHYCE A 175 
on other seaweeds, consisting of a single layer of 
cells. 
Usually there is no definite or characteristic 
arrangement of the cells, but in Zea, a genus much 
Fic. 54,—Letterstedtia insignis. Reduced. 
resembling Enteromorpha, and sharing its tubular 
character, there are groups of four cells arranged in 
quadrants, and in Hnteromorpha longitudinal rows of 
cells may be traced. The cells contain each only 
