Humphrey : OBSERVATIONS ON Gigartina exasperata HARV. 603 



ity and strength. The epidermal cells throughout the entire 

 plant are enveloped by a firm cellulose sheath of variable 

 thickness, from three to ten mic. (PL 42, Fig. 4, a.) This 

 cuticle is somewhat elastic, smooth and highly transparent. 

 PI. 42, Fig. 5, a and 6, represent surface views of a portion 

 of the frond, showing epidermal cells as seen through the 

 overlying cuticle. By focusing, deeper cells beneath the epi- 

 dermal layer may be seen. 



Beneath the epidermal cells and in connection with them are 

 the pseudo-cortical cells, presenting an almost spherical outline 

 and a somewhat loose though definite arrangement. These 

 cells as well as the epidermal ones are densely filled with pro- 

 toplasmic contents, though unlike the epidermal cells they con- 

 tain no chromatophores. 



The sections of the stipe were stained with an alcoholic so- 

 lution of methyl blue which gave a very satisfactory cellulose 

 reaction and revealed the fact that all the cells were imbedded 

 in a dense gelatinous matrix between which and the cell walls it 

 is not easy to distinguish. 



Adjoining the pseudo-cortical cells and occupying the cen- 

 tral region of the stipe is the pseudo-medullary area composed 

 of irregular cells. PL 42, Fig. 3, and PL 42, Fig. 4, represent 

 transverse and longitudinal sections of the stipe. In PL 42, 

 Fig. 3, c, a network of somewhat filamentous cells is seen to 

 be interwoven with other cells of different form forming alto- 

 gether a rather loose arrangement. 



Lamina. The general shape of the lamina is almost in- 

 variably cuneate, attaining its greatest diameter a little way 

 from the apex. In all cases the frond is flat and not greater than 

 three mm. in thickness, and when dry is quite translucent. 



It commonly grows from 30 to 50 cm. in length and from 6 

 to 18 cm. in width, thus showing considerable variation in size. 

 In shape it is quite as variable ; some fronds being branched pro- 

 fusely while others show little or no branching whatever. 



New fronds arise from the base of the stipe forming at first 

 somewhat club-shaped or pointed bodies, but later expand and 

 assume the characteristic shape of the mature frond. (PL 42, 

 Fig. i.) Both sides of the frond, including the margin, are 

 thickly studded with cystocarps and numerous epidermal prolif- 

 erations. Near the base of the frond on each side is a small 

 area totally void of proliferations. Here the frond is thicker 



