42 On the occurrence of Mannite in Laminaria Saccharina. 
though I should think scarcely half as much as what exists in the 
L. saccharina. 
Halydris siliquosa.—The next sea-weed examined was the Haly- 
dris siliquosa. With hot water it forms a very dark-coloured solu- 
tion, of a bitter and slightly astringent taste. The quantity of man- 
nite contained in it is very great, amounting, I should think, to be- 
tween 5 and 6 per cent. As already mentioned, mannite forms a 
great part of the white incrustations which appear on the surface of 
this sea-weed when dried. 
Alaria esculenta.—This beautiful sea-weed, which is by no means 
uncommon on the coasts of Scotland, where, as its name imports, it 
often serves as an article of food, also contains mannite in consider- 
able abundance. 
Rhodomenia palmata.—Rhodomenia palmata, or common dulse, 
contains a good deal of a sweet-tasted greenish-coloured mucilage. 
It also yields a considerable quantity of mannite, amounting pro- 
bably to 2 or 3 per cent. 
Fucus vesiculosus.—The Fucus vesiculosus, the most common, 
perhaps, of British algae, contains, I should think, from 1 to 2 per 
cent. of mannite; and the Fucus nodosus, also a very common sea- 
weed, likewise yields a small but very appreciable quantity of the 
same principle, 
Fucus serratus.—T his sea-weed also contains a considerable quan- 
tity of mannite, less, perhaps, than the L. digitata, but more than 
the Rhodomenia palmata. The mannite which the Fucus serratus 
yields is much freer from colouring matter than that from any of 
the other algae, being nearly colourless from the first. 
I could not detect any mannite in the Ulva latissima or Laver. 
The experiment was made on a very small scale, and will be repeated 
on the first opportunity. The Laver contains a good deal of a sweet- 
tasted green-coloured mucilage, similar to that of the Rhodomenia 
palmata. 
As mannite has occurred in eight out of nine of the sea-weeds 
which I have happened to examine, it probably exists in larger or 
smaller quantity in most sea-weeds, in which it appears to replace 
the cane and grape sugar, so abundant in many of our land plants. 
It is evident, also, that mannite occurs much more plentifully in 
nature than has been hitherto imagined. The following is a list of 
the algae just described, arranged in order according to the quantity 
of mannite which they severally contain :— 
1. Laminaria saccharina. 5. Alaria esculenta. 
2. Halydris siliquosa. 6. Rhodomenia palmata. 
3. Laminaria digitata. 7. Fucus vesiculosus. 
4, Fucus serratus. 8. Fucus nodosus. 
The quantity of mannite in the L, saccharina is such that I think 
