294 MINNESOTA BOTANICAL STUDIES. 



over the cystocarp. Dimensions of spore, length 20 to 35 mic. 

 width 13 to 20 mic. 



Young cystocarp material was collected late August, 1902, 

 showing the oogonium and accessory cells in figs. 16 and 17. 



The stages of development described in Callymenia J. Ag. 

 by Bornet could not be made out. 



Parasites. 



Microcladia coulteri. — This plant occurred parasitic on 

 nearly every plant collected. The largest found was six cen- 

 timeters in length. It is usually found on the margins of the 

 fronds but sometimes occurs on the surface. A section through 

 the lamina of the host shows the rounded base of the parasite 

 standing in a cup-like depression of the host thallus formed by 

 the disappearance of the epidermal cells. Long rhizoid-like 

 cells project from the short rounded cells at the base of the 

 parasite down between the cortical cells of the host {Plate 

 XL V., fig. 1). 



Callithamnion sp. — Almost all laminae showed at some 

 point traces of this parasite. The primary frond is frequently 

 covered with a fine short downy mat of it. Plate XLV., fig. 2, 

 shows a young filament extending up from the surface of the 

 host thallus. Beneath the surface the parasite sends down a 

 long rhizoid to the pith strand of the host through which it 

 ramifies. This rhizoid sometimes branches in the pith strand. 

 Above the surface the Callithamnion shows its characteristic 

 branching. Plate XLV., fig. 3 shows this parasite in the tetra- 

 gonidial condition. 



Comparison of Microcladia and Callithamnion. — The former 

 is comparatively large, is borne on the margin of the thallus and 

 its penetration into the pith strand was slight, not branching in 

 any direction. The latter was either invisible to the naked eye 

 or appeared as minute down on both surfaces of the host thal- 

 lus. It penetrated through all parts of the host as a single 

 branching filament. 



Porphyra sp. — Young Porphyra plants were found growing 

 epiphytically upon this parasitic Callithamnion. Plate XLV., 

 fig. 4, shows such a plant consisting of a filament of four cells 

 which broadens out to form the characteristic flat thallus of Por- 

 phyra. At the base the filament forks, forming two branches 

 of three cells each, which served as a holdfast. 



