62 



appear as slight points and upon sectioning through the frond at 

 the point of growth of such young specimens, it will be seen that 

 by the greater portion of the plant, at that stage, consists of the 

 rhizoidal filaments which penetrate deeply into the medullary tissues 

 of the host. The rhizoids are neatiy simple or with few branches, 

 and are red in color. As the parasite grows, more rhizoids are pro- 

 duced from the horizontal filaments which spread out radially on 

 the host-plant from the point of infection. From the horizontal fila- 

 ments, which form a sort of basai membrane, there arise, also, ver- 

 tical filaments, which are simple, three or four cylindrical cells in 

 height, and deep red in color. The vertical filaments are firmly ag- 

 glutinated together. The only organs of reproduction so far disco- 

 vered, are tetrasporangia. These arise from the basai cells of the 

 vertical filaments, are elongated ellipsoidal, and transversely divided 

 (zonate) into four tetraspores. They are well included within the 

 mass of vertical filaments. 



The plant just described differs from , the species of Cruoria 

 in its possession of rhizoidal filaments associated with its parasitic 

 habit. It bears a similar relation to Cruoria to that which species of 

 Actinococcus bear to the genus Petrocelis, although in the latter 

 case, there are differences in the number of tetrasporangia in a fi- 

 lament, etc. 



Specimens of this plant have been distributed in Collins, Holden 

 and Setchell, Phycotheca Boreali-Americana, N. 1049, 1903, under 

 the name of Pevssonneliopsìs epiphytìca Setchell and Lawson, mscr., 

 but without description. The full description is given below. 



Peyssonneliopsis Setchel! and Lawson mscr. 



Genus novum Squamariacearum et Cruoriearum. 



Parasitic, forming small dark red pustules, scattered over the 

 surface of membranaceous Rhodophyceae, sending rhizoidal filaments 

 deep into the tissues of the host-plant. Fronds composed of three 

 sets of filaments: 1) Rhizoidal filaments slender, sparingly branched, 

 penetrating into the centrai tissues of the host-plant; 2) Horizontal 

 filaments radiating, septate, sparingly branched, and forming a basai 

 layer a single celi thick; 3) Vertical filaments, arising from the cells 



