462 Johnson. — Two Irish Brown Algae: 
medullary cells (Fig. 9). These endophytic or intra-cortical 
hyphae can be traced from one surface to the other of Alaria , 
and there is every indication that they can, after creeping 
some distance, emerge at the surface of Alaria to form new 
tufts of Litosiphon . I took the opportunity, in describing 
similar phenomena in P. hibernicum , to refer to an important 
paper on parasitic Brown Algae by C. Sauvageau 1 , and content 
myself now with saying it is an important paper which has 
not received the attention in this country which its importance 
deserves. I have no doubt of the distinctly injurious effects 
of the innumerable tufts of Litosiphon on the thallus of Alaria. 
This injury is not due, apparently, to any special absorption 
of food-matter by parasite from host, but rather to an extreme 
type of ‘ Raumparasitismus.’ I have, for example, seen at 
Bundoran, this September, plants of Alaria in which the 
thallus, or what was left of it, was full of holes due to Litosi- 
phon-tufts, and others in which very little was left but midrib, 
and ragged ribbons of infested thallus. Whether this form 
of parasitism produces any degradation or not in Litosiphon , 
I cannot say. 
Summary. — The larger size of the filaments, their more 
distinct subarticulate appearance, and the large medullary 
cells of the filaments in L. Laminar iae , together with the 
differences in the arrangement of the reproductive organs in 
L. Laminar iae and P. hibernicum , are sufficient to justify their 
separation from another as species 2 . If the differences are not 
of generic rank and suppression must occur, I should prefer 
the execution to take place by the hand of Reinke, who, in 
founding Pogotrichum, pointed out the possibly modifying 
effects of a fuller knowledge of the nature of Litosiphon 3 . 
1 C. Sauvageau, Sur quelques algues pheosporees parasites, in Journal de 
Bot. vi., 1892. 
2 Batters in Grevillea (104, p. 118) had already, in reviewing my former paper, 
expressed this opinion tentatively. 
3 Prof. Reinke tells me his eyesight is now such that he is quite unable to 
carry on finer microscopic investigations : even writing is painful. If Pogotrichum 
be suppressed, he for one will rejoice that there is one useless genus the less in the 
world. 
