98 M. FOSLIE. [1905 



quently of a length IV2 the breadth, being 12 — 18 ft long and 

 9 — 15 i-t broad. In a vertical section the basal cells are partly 

 squarish, partly slightly horizontally or vertically elongated, 8 — 14//. 

 in diameter. The heterocysts are 22 — 36 //- long and 12 — 18 \i 

 broad. In specimens from other places and on other host plants, 

 1 have found the cells partly being a little smaller than the said 

 measures (e. g. once on Fucus vesiculosus) , partly a little larger 

 (e. g. on Zostera), the length being twice, and exceptionally even 

 twice and a half the breadth, up to about 24 //- long and up to 

 18 fi broad. Also the heterocysts will become larger or up to 

 40 //■ long and up to 30 //• broad, though they are mostly smaller. 

 They are rather varying, partly rather narrow proportionally to the 

 length, partfy very broad and both in f. typica and in f. calli- 

 thamnioides occasionally almost circular in shape. The latter partly 

 appear in large numbers, partly they may be few in number and 

 hardly traceable. The solitary small cortical cells are frequently 

 semicircular and distinct, sometimes, however, rather indistinct and 

 resembling those of M. Lejolisii. The conceptacles of sporangia 

 and cystocarps are hemispherical, sometimes hemispheric-conical, 

 scattered or somewhat crowded, 140 — 200 or up to 250 /^ in dia- 

 meter. The sporangia are four-parted, 50 — 90 //. long and 30 — 50 y. 

 broad. The conceptacles of antheridia are of the same shape as 

 the preceding ones, but only 60 — 80 //- in diameter. 



The form borealis is distinguished for a little coarser frond, 

 which seems to be more incrusted with carbonate of lime than 

 that of the typical form, and a little smoother. A new crust is often 

 developed over the primary one, and of about the same extent as 

 the latter. The cells are of about the same shape and size as 

 f. typica. The conceptacles are, as a general rule, larger, 200 — 

 300 \i in diameter. 



I have found f. borealis at Roundstone on the West coast of 

 Ireland, growing scantily on Gigartina mamillosa and on the leaf 

 of Laminaria saccliarina, partly associated with M. Lejolisii. Its 

 occurrence on the coasts of Denmark, Norway and Sweden is 

 unsure, the form occurring there perhaps belong wholly or in part 

 to M. Lejolisii. From Denmark (Nykjobing Mors) I have thus 



