160 MINNESOTA BOTANICAL STUDIES. 



after twenty-four hours re-examined. It was then found that 

 the cell walls were all dissolved and only the rings remained 

 (Fig. 17, PL 14). This leads to the conclusion that the rings 

 are not of the same composition as the cell wall. 



The pith of the cystocarpic proliferations of the frond shows 

 a marked difference from that of the vegetative portion (Fig. 

 18, PL 14). The cells have become very irregular in outline 

 and are so anastomosed and interwoven as to form a network 

 which becomes more and more dense in passing from the stalk 

 to the pericarp proper. Here, as well as in the cortex, the cell 

 contents have a dense granular appearance, and the cell walls 

 appear only very faintly, if at all. In most sections stained as 

 in the vegetative part they cannot be distinguished. This is true 

 also of the protoplasmic pits, though it is evident there is close 

 communication throughout. From one or two unusually clear 

 sections it was ascertained, however, that the rings are present, 

 but are very small. The cells in this region measure from 25 

 to 37 mic. long by 2.5 to 7 mic. wide. 



Cortex. The transition from the pith to the cortex is some- 

 what abrupt. In longitudinal sections the pith cells are seen to 

 decrease in length until in the four or five outermost rows the 

 outline of the cells is spherical or slightly oblong. In the transi- 

 tion zone; or the inner part of the cortex, they measure from 

 5 to 12 mic. along either diameter. 



In the outermost layers of smallest cells, measuring from 2.5 

 to 5 mic. in diameter, the cell contents are very dense and the 

 cells are apparently imbedded in a gelatinous matrix from which 

 it is impossible to distinguish their walls. In one section, how- 

 ever, the writer was able to make out faint outlines of the walls, 

 but it is difficult to represent them and maintain the proportional 

 thickness of the wall (Fig. n, PL 13). 



The cortex cells are seen to lie in communication also, but 

 only along the radial lines of the thallus. The cells are so 

 small no rings can be distinguished, but protoplasmic threads 

 are seen running from cell to cell (Fig. 13, PL 13). There are 

 no lateral protoplasmic connections between cells. A surface 

 view of the thallus shows a somewhat regular arrangement of 

 the end cells of these radial rows. They appear as a rule in 

 groups of two or occasionally three, surrounded by the gelatin- 

 ous matrix (Fig. 14, PL 14). If the sections be placed in water 

 this swells rapidly, as do also the cell walls. The walls often 



