Holtz : OBSERVATIONS ON PELVETIA. 



DESCRIPTION OF PLATES. 



PLATE VII. 



Photograph of single plant of Pelvetia fastigiata. Shows hold- 

 fast, bifurcation of stipe and of laminae. The warty appearance of 

 some older laminae is due to papilla? caused by conceptacles. Several 

 laminae have burst open through absorption of water, and show the 

 conceptacles on the inner side of the cortex. About one half natural 

 size. 



PLATE VIII. 



Photograph showing bed of Pelvetia fastigiata on the rocks at Port 

 Renfrew, exposed at ebb tide. This photograph was taken by C. J. 

 Hibbard for the Botanical Department of the University of Minnesota. 



PLATE IX. 



Anatomical detail : All drawings were made with the aid of camera 

 lucida, diagrams excepted. All on this plate about x 250. 



1. Shows part of the cross-section of stipe from epidermis to center 

 of stipe. 



2. Longitudinal section of stipe, showing cells with protoplasm, 

 nuclei and chromatophores. The protoplasmic connection between 

 cells is indicated. The cuticle covers the epidermis. 



3. Cross-section of lamina. Shows the large amount of intercel- 

 lular jelly in the pith region. 



4. Longitudinal section of lamina, showing anastomosing pith cells. 

 The space between them is filled with intercellular jelly. 



5. Diagram of longitudinal and cross-section of stipe or lamina. 

 Shows radially elongated epidermal cell. Beneath this are six or 

 more rows of cortex cells and beyond these the pith. The cortex is 

 shown arising as a basal cut-off of the epidermis. Previous cut-offs 

 are shown in different stages of growth and division. Growth is prin- 

 cipally in periclinal and longitudinal directions. The outer cells are 

 more regularly rectangular, but become more rounded on the edges 

 and corners toward the pith. The inner cortex rows finally become 

 modified into long, cylindrical pith cells. The cells are separated 

 farther by intercellular jelly as the pith is approached. 



6. Vertical section through central part of holdfast. The lower 

 part is shaded to show that the cells are dead, elsewhere also where 

 such cells occur. The basal cells are flattened. The walls of the dead 

 cells are gelatinous. The cells are shown with chromatophore masses 

 to help indicate division. In the upper part the cells are elongated. 

 Here the stipe begins. 



