210 MINNESOTA BOTANICAL STUDIES. 



differ considerably in other respects also, from the central cells. 

 The outer cells are more flattened than the central ones, they 

 are more densely protoplasmic and are filled with grains of 

 floridian starch, while but little starch occurs in the central cells. 

 In this more superficial portion of the central area the proto- 

 plasmic connections between the cells of the filaments of which 

 the tissue is composed can be easily made out. They are 

 plainly visible in both stained and unstained preparations, and 

 in both tangential and cross sections. In accordance with the 

 less dense protoplasmic contents of the central cells, the con- 

 necting strands are less evident among them, but when the walls 

 of this area are stained, numerous pits are shown penetrating 

 the walls of the central cells (Fig. 3). These pits appear to be 

 of irregular distribution and often more than one are to be ob- 

 served between the same pair of cells. They can be best ob- 

 served in a tangential section. 



{b) The cortical area consists of small cells almost spherical 

 or with the longest diameter perpendicular to the surface of the 

 frond, of quite uniform size (averaging 5.7 X8.5 mic), arranged 

 in 1-3 layers, either in filaments perpendicular to the surface of 

 the frond or somewhat irregularly. In a surface view of the 

 lamina they appear entirely irregular in arrangement (Fig. 4). 

 The cells are densely protoplasmic and contain chromatophores. 



Stipe. — The general structure of the stipe (Fig. 5) is similar 

 to that of the lamina, but there are numerous special modifications 

 of the several areas. The cells of the central area are elongated 

 somewhat in the direction of the axis of the frond and are some- 

 what compressed parallel to the compression of the stipe. 

 They are of more uniform size than were those of the lamina, 

 and they were otherwise more nearly uniform than those of the 

 lamina. Their average size is 57 x86 x 143 mic. The cortical 

 area of the stipe is much thicker than that of the lamina. It is 3-8 

 cells deep. The cells are larger than the corresponding cells 

 of the lamina (average 14x23 mic.) and are conspicuously ar- 

 ranged in filaments running perpendicular to the surface of the 

 stipe. 



Proliferations. — The structure of the proliferation is similar 

 to that of the main frond. The central cells are somewhat 

 elongated in the direction of the axis, and, in general, are more 

 numerous and smaller than the corresponding ones of the main 

 frond. All the cells except those of the cortical area contain 

 considerable floridian starch. 



