PROTOPLASMIC CONTINUITY IN THE FUCACE^E. 99 



until they pass over iuto the filamentous tissue of the the centre. 

 The cell walls attain considerable thickness, and the protoplasm is 

 granular and of a brown colour. Towards the centre the colour 

 becomes less pronounced, and almost or entirely disappears. 



An important feature of the cortex is the presence of numerous 

 lateral diverticula, which connect the cells of the successive layers 

 transversely, so that the whole tissue forms a cell complex, whose 

 elements are closely interconnected. The outermost cortical layer 

 is connected in a similar manner with the epidermis. 



The Central Tissue. — Towards the centre of the thallus the 

 cortical cells pass over into long filaments with thick walls, which 

 make up the major part of the central tissue. There is, however, 

 no distinct line of separation between the cortex and this tissue. 

 The filaments run for the most part longitudinally, and more or 

 less parallel to one another. They arc composed of cells, 0*001 

 inch in breadth and 0.003 inch in length, on an average, joined 

 end to end, whose outer boundaries are usually lost in a gelatinous 

 or cartilaginous matrix. The protoplasmic contents are very 

 gaanular, but the brown colour of the outer parts of the thallus is 

 nearly or altogether absent. Numerous transverse diverticula 

 connect the filaments laterally with one another, and the outermost 

 with the cortex, so that the whole has more or less of a reticulated 

 appearance. 



Beside the filaments that run longitudinally, the central tissue 

 contains other structures of a more fibrous character. These 

 arise from the cortical cells, curve inwards towards the centre of the 

 thallus, and form a sort of " weft " to the filamentous " warp." 

 They resemble the filaments in general appearance, but their walls 

 are much thicker and the protoplasmic contents are correspond- 

 ingly attenuated. Though very fibrous in aspect, they are made 

 up of cellular elements, the transverse petitions being very oblique 

 and not perpendicular to the side walls as in the filaments. 

 PI. 255, Fig. 1 (a). The walls of the fibres are very beautifully 

 laminated, and exhibit a very peculiar annulation which the writer 

 has not met with in any other group of plants. As shown in 

 Fig. 8, it presents itself as a number of ring-like ridges developed 

 on the outer surface of the fibre. It was at first imagined that 

 these had some connection with the division of the cells, and the 

 formation of the sieve-plates described below. But the rings 

 formed round the sieve-plates are formed on the inner surface 

 of the wall, the outer surface taking no part in their formation. 

 Sometimes there are two, three, or more of these external rings 

 pretty close together, but in others they are placed singly, at a 

 distance from one another. 



In good sections prepared by either of the methods A or B, or 

 indeed by any process which ensures a slight contraction of the 

 protoplasm, a suspicion of the existence of continuity will be 

 created by the appearance of the cell-contents, both in the cortical 

 and the central region. For in typical cases the contraction is for 

 the most part lateral and not Ivngitudinal, so that although the 

 contents retire a little from the side walls of the cells, they usually 



