PKOTOPLASMIC CONTINUITY IN THE FUCACE^. 355 



HiMANTHALIA LOEEA Lyilgb. 



The stalked, funnel-shaped thallus of this "weed," witli its 

 coriaceous fruit-body divided dichotomously into thong-like branches, 

 is a well-known inhabitant of British coasts. In its mode of repro- 

 duction and general structure it closely agrees with the Fucacece 

 already dealt with, and with which systematists usually associate 

 it. The thallus is composed of Epidermal, Cortical and Central or 

 Medullary tissues, though there is no sharp line of distinction 

 between them. Save in the presence of the conceptacles bearing 

 antheridia or oogonia, the reproductive part, which constitutes by 

 far the major portion of the thallus, has substantially the same 

 structure as the sterile part. 



The Epidermal tissue is composed of several layers of cells, 

 often so connected with one another that the cells of each layer 

 appear to arise by the dichotomous branching of those of the next 

 inner layer. The cells of the outermost layers have their longest 

 diameter perpendicular to the surface of the thallus, and their 

 narrow, oblong, or wedge-shaped protoplasts forcibly remind one of 

 the columnar epithelium of animal mucous membranes. 



The Cortical tissue is a thick parenchymatous mass, whose con- 

 stituent elements vary in size and shape, and in the thickness of 

 their walls. Small where they abut on the epidermal tissue, they 

 become longer and stretched in the longitudinal direction, towards 

 the interior, and finally pass over somewhat abruptly into the fila- 

 ments and fibres which constitute the central tissue. The proto- 

 plasts are irregular in shape, and send out radiating pseudopodia- 

 like processes in various directions. Transverse and longitudinal 

 sections show that the cell-walls are more strongly thickened in 

 the middle region of the cortex than in the inner and outer 

 portions. 



The Central tissue, like that of other Fucoids, is composed of 

 cellular, filamentous structures, which originate, at least in part, as 

 outgrowths from the cortical cells. These are loosely interwoven 

 longitudinally and transversely, though the great majority run in 

 the former direction. Two kinds may be distinguished, viz., fila- 

 ments proper and fibres. The former are stouter, have more homo- 

 geneous walls, and more watery protoplasmic contents. Their 

 articulations are provided with a thick annular ingrowth, which 

 surrounds the transverse partitions where such are present. A 

 constriction of the outer surface, at irregular intervals, is a common 

 phenomenon in these filaments. The fibre-like structures are 

 finer, and have very dense protoplasmic contents, while their walls 

 are longitudinally laminated. At intervals, which are sometimes 

 considerable, are placed transverse septa, which are extremely 

 oblique, tbe fibres in this, as in other characters, resembhng the 

 fibres described and figured in Ascophijlluja nudusum.* Both fila- 

 ments and fibres branch more or less freely, but the former are not 

 connected with each other by lateral diverticula, as are those of the 

 plant named. 



* Loc. cit,, p. 99. 



