Pogotrichum and Lito siphon. 461 
present in a filament, and to which the term isosporangiate 
may be applied. The anisosporangiate state is, of itself, 
sufficient to justify the separation of P. hibernicum from 
L. Laminariae as a species. It is, however, not merely of 
systematic value. It is of interest in connexion with the 
discussion of the modes of reproduction 1 in Phaeophyceae 
by unilocular and plurilocular sporangia, and is not without 
significance in reference to theories of reproduction in the 
lower plants generally. No doubt a full knowledge of the 
fate of the contents of the sporangia would be of great interest. 
Thallus. — A difference of considerable importance in dis- 
cussing the affinities of these plants exists in the structure 
of the thallus. In P. hibernicum and in L. Lojninariae the 
filaments are multicellular, usually pluriseriate. But while 
in P. hibernicum the internal cells are not markedly dissimilar 
to the external ones, in L. Laminariae the central axial cells 
are much larger than the peripheral ones, and by their 
horizontal cross-walls and subverticillate hairs give to the 
filaments a zoned appearance (Figs. 7, 8). 
Vegetative reproduction. — L. Laminariae differs from Z. 
pusillus , as P. hibernicum does from P. filiforme , in being of 
endophytic habit. The earlier description 2 of this habit in 
P. hibernicum will apply equally well to L. Laminariae. 
The filaments of a tuft are unbranched and to this extent 
unconnected ; they are, however, at their lower ends in close 
contact with one another and more or less fused into a com- 
pact body of a subparenchymatous nature. There are to 
be observed, growing out from the superficial cells at the base 
of the filaments, rhizoidal septate hyphae which come into 
contact with the surface of Alaria , and can no doubt, as in so 
many Phaeophyceae, give rise to new Zz/<?.s7)>A?/2-plantlets. 
On making a vertical section of Alaria through the anchorage 
of a Litosiphon- tuft, the individual filaments and rhizoidal 
hyphae of Litosiphon are seen to penetrate into the Alaria - 
thallus, to creep and ramify between the cortical and the 
1 E, Bornet, Note aux quelques Ectocarpus. 
3 T, Johnson, Proc. Roy. Dublin Soc,, n. s., I. i, p. 2. 
