460 Johnson . — Two Irish Brown Algae : 
in my summary I say, ‘ P. hibernicum is very near to, if not 
identical with, Litosiphon Laminariae I have within the 
past two or three years had several opportunities of collecting 
living material of Alaria infested sometimes by P. hibernicum , 
sometimes by Litosiphon Laminariae. Examination of this 
material has given me surprising results, explaining my diffi- 
culties in the examination of the herbarium-material, and 
justifying my earlier attitude. 
Sporangia. — The filaments in the tufts of L. Laminariae , 
which are scarcely distinguishable to the naked eye from 
those of P. hibernicum , are fertile, generally abundantly so, 
and each filament possesses both unilocular and plurilocular 
sporangia (Figs. 5, 6, 7), a condition of things which is, 
I believe, unparalleled 1 . The lower half of the filament is 
usually purely vegetative, and the upper reproductive (Fig. 8). 
The unilocular and plurilocular sporangia have no regular 
arrangement ; they are frequently intermixed in a most 
indefinite manner, standing singly or in groups, side by side, 
or separated by more or fewer sterile cells. They are derived 
from intercalary and sub-terminal superficial single cells or 
cell-surfaces. In all essential features the individual unilocular 
and plurilocular sporangia of Litosiphon Laminariae are like 
those of Pogotrichum hibernicum . They differ in occurring 
side by side on the same filament, not on distinct filaments 
as in P. hibernicum. 
It will be convenient to speak of the filaments of L. La- 
minariae as anisosporangiate 2 in contradistinction to those 
of P. hibernicum in which sporangia of one kind only are 
1 On comparing the superficial appearance of a fertile part of a filament of 
L. Laminariae with a sterile part, it is easy to see how, in earlier times, with less 
perfect microscopes, the individual compartments of a plurilocular sporangium 
were mistaken, in filaments with obvious unilocular sporangia , for the large 
chlorophyll-grains, and L. Laminariae has thus continued to the present day to 
be described as possessed of unilocular sporangia only. Harvey in all probability 
saw the plurilocular sporangia, for in describing L. Laminariae he states that 
‘ the (peripheral) cells sometimes separate into four smaller cells which occupy the 
same space,’ a condition represented in the illustrations. Lyngbye and J. G. Agardh 
both speak of the granula being quaterna or subquaterna. 
2 The term heterosporangiate has already a definite signification. 
