672 MISS RATHBONE ON MYRIACTIS ARESCHOUGTI 
though this time numerous small alge with penetrating rhizoids 
were found on the thallus, it was impossible to decide whether 
they were really 1/7, Areschougii in its early stages or one of the 
numerous other parasites by which its host is infested. As, 
therefore, it seemed hopeless to try to determine the young 
stages of this species by any method but that of pure cultures, 
which under the circumstances would have been difficult, if not 
impossible, the work was necessarily confined to a study of the 
older stages. 
Nothing is positively known about the first entrance of the 
parasite into the host, but presumably this takes place, as 
M. Sauvageau suggests, by means of zoospores. The theory 
that these enter by means of the cryptostomata or conceptacles 
seems hardly tenable, as in Himanthalia cryptostomata only 
occur on the very young receptacles, the hairs being shed at an 
early stage and replaced by the organs of fructification. The 
cushion of MM. Areschougii is not sunk so deeply in the host- 
tissue as are the conceptacles, and the plants do not appear to 
be connected with these in any way; indeed, I have seen a tuft 
growing close to the edge of a conceptacle without entering it, 
and the rhizoids of the parasite often work their way among the 
cells surrounding a conceptacle without penetrating into the 
cavity. 
The few rhizoids which start from the base of the cushion soon 
branch, and travel for long distances in the host-plant, some 
twisting and twining among the filaments of the loose central 
tissue of the Himanthalia, and others, working their way through 
the cell-walls of the denser elements bordering this, form here and 
there small knots which stain deeply with iodine or Hoffmann’s 
blue (Pl. 24. figs. 2 & 3). In fresh material these rhizoids are 
easily distinguished from the host-tissue by their pinkish-brown 
colour, and in sections treated with aqueous solutions of methyl- 
violet or methylene-blue, those rhizoids which are wandering about 
in the loose central tissue stain less deeply than the filaments of 
the host, and, in the case of the methyl]-violet, assume a bluer 
tint. Under the action of these reagents the rhizoids take on a 
characteristic appearance, owing to the deeper staining of certain 
small granules in the protoplasm. With methyl-violet and 
methylene-blue, the Himanthalia-tissue itself is too deeply dyed 
to allow the passage of the parasitic filaments between the 
cell-walls to be traced ; but with Hoffmann’s blue the penetrating 
