158 MINNESOTA BOTANICAL STUDIES. 



cells containing the chromatophores. Because of this dif- 

 ference in the cells the sections for the structure of the stipe 

 and lamina show the outlines of the cell wall in the pith, but in 

 nearly all the sections examined the cell walls of the cortex 

 could not be distinguished, and it is the outline of the cell con- 

 tents that is represented in such sections. 



The inner portion or pith consists of elongated, cylindrical 

 cells, united into loosely interwoven filaments, extending prin- 

 cipally in the direction of the long axis of the frond. The 

 union between cells is so irregular that often the filamentous 

 arrangement is scarcely recognizable. Surrounding this pith 

 region, which is of compressed cylindrical contour in the stipe, 

 is the cortex, which consists of much smaller cells, arranged in 

 radiating rows, more or less regular, perpendicular to the sur 

 face of the frond. 



Pith. — The transverse sections of both stipe and lamina show 

 the cross-sectional outline of the pith cells to be more or less 

 circular with considerable space between the cells (Figs. 12 and 

 13, PL 13). In the lamina portions of a filament are often 

 found running through the section. The outlines of the pith 

 cells in both lamina and stipe show an area of larger cells just 

 within the cortex, passing inward to a central portion of smaller 

 diameter (Fig. 11, PI. 13). Within the pith itself there is con- 

 siderable variation in the size of the cells, showing that smaller 

 filaments anastomose with the larger ones. 



The average size of the cells is from 100 to 170 mic. long by 

 ^7 to 33 mic. wide. The most interesting feature of the pith is 

 the presence of protoplasmic pits connecting the cells. These 

 occur not only in the end walls, but also in the lateral walls, as 

 seen in Fig. 11, PI. 12. By these connections, as well as by 

 lateral pressure in some cases, the cylindrical outline of the 

 cells becomes variously modified. 



Communication of adjacent cells of the pith region is thus 

 completely established. The significance of this will be more 

 clearly seen as the physiological importance of this area is dis- 

 cussed. These pits were first discovered by staining with heema- 

 toxylin. A more careful trial of different stains showed that 

 these pits always take the stain more deeply than any other part, 

 either cell contents or cell wall. Both methyl violet and fuchsin 

 produced good results. An alcoholic solution of the stain was 

 used. 



