HoltZ : OBSERVATIONS ON PELVETIA. 29 



shape as the outer cells of the cortex are approached. Here 

 they appear to be simply the original dividing wall. They can, 

 however, be located by the protoplasm apparently running right 

 through the wall at these places. This apparent communica- 

 tion of the protoplasm of adjoining cells was observed as far out 

 as the second layer of cells below the epidermis. Farther out 

 this could not be seen on account of the chromatophores. But 

 probably even the epidermal cells communicate with each other. 

 The concentrated sulphuric acid test showed that the plates 

 were dissolved as well as the rest of the wall. No positive 

 proof was found that the pits were perforated, no threads of 

 protoplasm having been observed, as would indeed be difficult 

 with the extreme thinness of the plates. But the symmetrical 

 arrangement or attachment of the protoplasm on both sides of 

 the pits leads one to suspect very strongly that there is com- 

 munication. By plasmolysis the protoplasm draws away from 

 the cell wall at all other points than the pits (Fig. /j). It 

 remains attached here and extends in ropes through the cells 

 and seemingly through the pits. The protoplasm often branches 

 to lateral pits (Fig. 14). When the pith cells are swollen in 

 fresh water the protoplasm is frequently torn off from one end 

 of the cell, away from a pit, owing apparently to the elongation 

 of the lateral wall as well as the gelatinous matrix. In such 

 cases the pit curves in toward the loosened protoplasm (Figs. 

 12, 14). 



Iodine is the most satisfactory stain to use in studying pits. 

 The protoplasm is stained and its attachments may be studied. 

 Pits and anastomosis may be nicely studied by removing some 

 of the protruding pith from a lamina that has burst in fresh 

 water. By flattening the gelatinous mass under the cover glass 

 the pith cells and their pits show up well, even unstained, though 

 better if differentiated with stains for walls and for protoplasm. 



Anatomy of Holdfast, Stipe and Lamina. The above mat- 

 ter on the tissues in the body of P.fastigiata needs some modi- 

 fication and addition when the holdfast, stipe and lamina are 

 considered separately. 



* Holdfast. In a vertical section through a holdfast it is seen 

 to be composed of approximately regular, ascending rows of 

 cells ; those near the central part more vertical ; those near the 

 border of the holdfast curving out as they go down. There is 

 a marked difference between the cells in the middle and those 



