240 University of California Publications in Botany [Vol. 8 



4. Monostroma areolatum S. and G. 



Plate 25 and Plate 28, fig. 2 



Frond very delicate, lubricous, 20-35 cm. high, sessile, saccate when 

 young, soon splitting and forming numerous, long, broadly ovate or 

 obovate, undulate, plicate and much crisped lobes, pale green; mem- 

 brane distinctly and finely areolate, 9-12/a thick; cells with rounded 

 angles, 6-7/a diani., subspherical in cross section, grouped within each 

 areole. 



Growing on' Zostera in quiet waters. Sitka, Alaska. 



Setchell and Gardner, Phyc. Cent. I, 1920, p. 281, pi. 30 and 

 pi. 31, fig. 2. 



This species of Monostroma is exceedingly beautiful and among the 

 most delicate and flaccid of the genus. The frond remains saccate for 

 a brief period only, attaining a height of but a millimeter or two. 

 The sack then breaks and the membrane spreads out at once, early 

 developing small lobes. Finally a few primary lobes are established 

 and these develop numerous secondary lobes. The growth on the 

 whole margin greatly exceeds that of the interior, which results in 

 the production of a great number of folds, making the margin very 

 much crisped. In the thickness of the frond and shape of the cells 

 M. areolatum closely approximates M. zostericola Tilden. The cells 

 of the latter are, however, more angular and more closely placed, and 

 the frond is not divided into areolae. There is a marked difference 

 in the size of these two species as well as in their method of develop- 

 ment. M. zostericola is diminutive, remains saccate for some time, 

 and then splits longitudinally, forming several lobes broadening out- 

 ward. M. areolatum very closely resembles the genus Prasiola in the 

 grouping of the cells as seen in surface view. 



5. Monostroma quaternarium (Kuetz.) Desmaz. 



Frond at first attached, soon becoming free, soft and delicate, 

 irregularly lobed and folded, 20-23/i, thick; cells rounded, when 

 actively dividing set closely in threes and fours within the mother cell 

 wall ; in cross section semicircular or oval, 15-17;Lt high. 



Floating in brackish and in fresh water. Washington to southern 

 California. 



