Splachnidium rugosuni. 3 



cells, which branch and anastomose irregularly (plate 1., fig. 2, a, b, c\ In 

 the young state there is active cell-division (plate II., fig. 3), and, as each 

 mature cell is greatly elongated, the granular protoplasm which at first fills 

 the whole cell becomes somewhat attenuated, and in some cases, though 

 this appearance is, perhaps, owing to the method of preservation, ruptures 

 altogether, so that a mass of protoplasm remains at each end of the cell 

 overlying the septum, and gradually tapering towards the centre of the 

 cell. The small filaments are produced from the large ones by lateral 

 branching ; the individual cells are very long, and the cell-cavity is small 

 (plate I., fig. 3, a, b, c, d). 



The disc from which the branches spring is like the rest of the thallus 

 in colour, brown or olive-green, and it has no special organs of attachment. 

 A section taken in any direction through the lower part, i.e., the region 

 below the origin of the branches, shows a mass of closely woven un- 

 branched septate filaments (plate II., fig. 6), with thick walls and a small 

 amount of cell-contents. These are woven together so that interhyphal 

 spaces are absent ; where they approach the surface, their arrangement is 

 looser and their apices project freely ; these latter contain a dense granular 

 protoplasm. As in the Laminariacece and Fucacecz, the plant is covered 

 with a mucilaginous substance. In Splachnidium rugosum this is very 

 abundant, and not only covers the outside of the thallus, but is largely 

 developed within, and fills the branches. On staining some of the filaments 

 with haematoxylin, the stain is taken up by an otherwise invisible sub- 

 stance, which surrounds them, forming a thick coating on the outside of 

 the wall. The same appearance shows itself on staining a piece of the 

 thallus. 



INCREASE IN LENGTH AND APICAL CELL. The chief increase in growth 

 of the plant takes place as the result of the activity of a zone of meristematic 

 tissue which surrounds the actual apical cell, and thus a contrast is offered 

 to the mode of growth which obtains in the Fucacece. The apical cell (plate 

 II., fig. 4), in Splachnidium rugosum differs entirely in appearance from the 

 surrounding meristem ; it has a pear-shaped body bounded by a thick 

 transparent mucilaginous wall, and a filiform basal process stretches 

 towards the interior of the thallus. This cell and the very active surround- 

 ing meristem are sunk in a slight depression ; the two outer layers of the 

 meristem by radial division form the epidermal cells, which continue to 

 divide radially until the part of the thallus in which they lie has reached 

 maturity. Some of the inner cells of the meristematic zone form the 

 adult cortical layers ; these are at first polygonal in shape, and when once 

 formed do not again divide, each increases in size and becomes oval ; by 

 subsequent separation of these cells the cortex keeps pace with the 



