6 | Scientific Proceedings, Royal Dublin Society. 
ericoides, and of Streblonemopsis irritans on Cystosira opuntioides. 
As the tufts of Pogotrichum hibernicum are very numerous, 
penetrate deeply into the host tissue, and occur, in my material, 
on very young plants, it would seem that there is a possibility of 
considerable injury being inflicted on the Alaria. Sauvageau 
traces in the plants examined by himself a gradation of parasitism, 
from the more or less symbiotic condition of Streblonemopsis irritans 
on C. opuntioides, to the well-marked parasitism of Zctocarpus 
investiens and of E. parasiticus, without seeing much indication of 
injury to the host-plants, or of degradation of the parasite. 
Reproductive Organs of P. hibernicum.—As already mentioned 
every epiphytic or extra-cortical filament is, judging from my 
material, fertile. One of the features which struck me most on 
first examining the plant was the very great abundance of the 
reproductive organs which are confined for the most part to the 
free (upper) halves of the filaments. In this region the whole of 
the superficial cells of the thick filaments, or in some cases, the 
whole of the internal cells also, and all the joint-cells of the 
uniseriate ones are not at all unfrequently converted into repro- 
ductive cells. Thus the sporangia stand side by side more or less 
continuously over the whole of the surface of the upper part of the 
filaments. One cannot speak of definite sori of sporangia as one 
does in such a plant as Dictyota. The zoosporangia are of two 
kinds: unilocular and multisporous (figs. 3, 4) and plurilocular 
(fig. 5). Both kinds occur in the same tuft, but not, so far as I 
have seen, on the same filament. Unfortunately I know nothing 
as to the fate of the zoospores. I hope to have an opportunity of 
examining them at Kilkee in the coming year. On comparing 
P. hibernicum with P. filiforme, Rke., it is found as described by 
Reinke, that P. filiforme, Rke., has no lateral Pheosporean hairs, 
has plurilocular sporangia only, and is entirely epiphytic on 
Laminaria saccharina. Its filaments are longer, thinner, and have 
their plurilocular sporangia more localized than is the case in 
P. hibernicum. As regards the absence of endophytic organs 
in P. filiforme, a parallel case is presented by Litosiphon, one 
species of which, L. pusil/us, is epiphytic, the other, L. Laminaria, 
1J. Reinke, ‘‘ Atlas deutscher Meeresalgen,’’ 11. 3, 4; s. 62. 
