4 2 



INTRODUCTION. 



kinoplasmic connecting fibers between the nuclei, and in the region of 

 the cell-plate the cytoplasm seems undifferentiated. The plasma mem- 

 branes, or cell-plates, which will separate the four spores, are laid 

 down almost simultaneously. In the region where they are to appear 

 the cytoplasm, as elsewhere, except near the nuclei, presents the same 

 visible structure of alveolae, or perhaps a mixture of alveolae and a 

 thread-like network. Rather large and small meshes are intermingled. 



FIG. 16. Cell-plate of Die tyota dichotama. and Stypoca-ulon. 



A, portion of cell-plate^ from tetraspore mother-cell of Dictyota, formed apparently by arrangement of 



alveolar lamellse into a continuous and even plane. 



B, same from apical cell of Stypocaulon. (B, after Swingle.) 







The small-meshed structure is apparently more granular than that 

 with larger meshes. 



The first visible trace of a cell-plate is manifested by the transverse 

 walls of the alveolae becoming perceptibly thicker and arranging them- 

 selves in such a way as to appear as an uneven or somewhat zigzag 

 line in section (Fig. 16, A). In this cell-plate primordium the walls 

 of both large and small meshes take part. At first certain of the alve- 

 olar lamellae are thinner than others, so that the cell-plate seems 



