Holtz: OBSERVATIONS ON PELVETIA. 27 



of growth ; and to some extent they divide both radially and 

 vertically, but not tangentially. These two rows of cells also 

 have rather thin walls, although there is some thickening at the 

 angles. They are also densely packed with chromatophores. 



Below the above-mentioned cells are three or four (five) con- 

 centric rows of cells that pass over into the pith on the inner 

 side. Their walls are considerably thickened with a gelatinous 

 substance, which, however, is firmer and denser than that of 

 the pith. These walls stain deeply. The cells of these rows 

 contain color grains but in more loosely disposed masses. The 

 protoplasmic sac is more easily seen around these masses of 

 chromatophores than in the outer cells. These cells have nearly 

 the same radial diameter as the cells in the second and third 

 rows, but are generally twice as wide tangentially and twice as 

 long vertically as those of the third row. There is more or less 

 variation in the number of rows of each of these different sizes 

 of cells. These elements may be diagrammatized as in PL IX. r 

 Fig. 5- 



The original walls between these cells thicken as the pith is- 

 approached. The cells lose their rectangular shape more and 

 more towards the pith till at last it is sometimes difficult to dis- 

 tinguish them from the more cylindrical pith cells. The cells 

 remain in communication through pits, the cells anastomosing 

 frequently. The longer cells form transverse septa, which are 

 often oblique to the lateral walls. These septa are never 

 thickened, but remain very thin and, to all appearance, allow 

 protoplasmic communication {PL IX., Fig. 12). 



Pith. — {PL IX., Pig's. 1-5 '.) The pith of the stipe and lamina 

 is distinguished by the fact that the cells are separated widely 

 by intercellular jelly, which in the lamina is from two to three 

 times as thick as the diameter of the cells imbedded in it, less- 

 thick in the stipe (1-2). The pith is also marked off by the 

 jelly not staining as deeply as the intercellular matrix in the 

 cortex. With some stains, fuchsine for example, the stain may 

 be almost completely removed by washing, leaving the inner 

 wall of the pith cells colored. Pith cells are slightly com- 

 pressed corresponding with the flattening of the stipe or lamina 

 {PL IX., Fig. /). They are nearly as wide as the average 

 width of the cortex cells, and are about as long or a trifle longer 

 than these. They are crossed by delicate septa {PL IX., Figs. 

 2, 4., ij). Pith cells are joined into vertical rows or filaments 



