250 



Prof. P. M. Duncan on Thallophytes 



o£ BryoiDsis living under extraordinary circumstances, or that it was a 

 modified form o£ it, especially as I noted instances where the filaments of 

 this plant had penetrated and perforated through projectiug nodules and 

 ridges of the hard parts of the coral. 



The adhesion of the Bryopsis would give the delicate filament about 

 to penetrate a point cVcipjmi. But on placing some tubes of Bryojpsis 

 which had short filaments on their outsides, like those obtained by decal- 

 cifying, in glycerine, this liquid speedily entered what appeared to be the 

 tubular structure of the plant, filled with dark green granules and 

 cytioplasm. It filled the tube and made the cell-wall sufficiently trans- 

 parent to show that there were no cell-contents, but numerous filaments 

 of an Achlyan-lookiug parasite. These had penetrated the Bryopsis, had 

 grown at the expense of its cytioplasm, and, finally, they were making 

 their way out through the wall and coming in contact with the coral. 



I have not been able to trace the mobile zoospores of the Achlyan or 

 the origin of parasitic filaments from them but it is evident that the 

 parasite exists on the outside as well as within the coral, and in the 

 tubular or vegetative form, and that the external filaments contain imma- 

 ture zoospores which develop tubules which penetrate the parent wall, 

 impinge against the coral, and penetrate (Plate 7. fig. 55). 



ym. Structure of Reproductive Elements and Classificatory Position. 



The parasites, whether enclosed within their tubular perforations, which 

 assimilate to their shape, or rendered visible by the action of dilute acid, 

 or when free on the outside of the corals, present the appearance of the 

 mycelium of fungi of such orders as the H^^homycetes and Physomycetes. 

 •The filaments, whate"^'er may be their diameter, are furnished with a 

 continuous cell-wall, and dissepiments are extremely rare, being only 

 recognized once or twice in hundreds of specimens. The filaments rarely 

 inosculate, but branch either rarely or with great frequency. There are 

 often secondary and other branchlets ; and the width of the calibre of the 

 whole tube is usually maintained. 



It is very usual for branching to take place at right angles to the 

 parent filament, and for a small rounded continuation of the last to form 

 beyond the ramification. 



More or less globular or hemispherical swellings occur on the side 'of 

 the filament, and occasionally it is swollen out into one or a succession of 

 spherical enlargements. The filaments terminate in culs-de-sac usually of 

 the same diameter as the rest of the tube ; but globular or iiTegular-shaped 

 enlargements are by no means uncommon at their ends. In all this the 

 parasite resembles many fungi. It is towards the ends of some smaller 

 filaments that a cell-dissepiment occurs, separating a terminal portion, 

 only filled with dark cytioplasm, from the rest of the filament, which often 

 contains a refractive fluid with large granules here and there (Plate 7. 

 figs. 49-61). 



