Laminaria saccharina and other Sea-weeds. 265 



tioned, 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 con- 

 tains mannite in considerable 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 probably to 2 or 3 per cent. 



Fucus vesiculosus. — The Fucus vesiculosus, the most common 

 perhaps of British Algse, contains I should think from 1 to 2 

 per cent, of mannite, and the Fucus nodosuSf also a very com- 

 mon sea-weed, likewise yields a small but very appreciable 

 quantity of the same principle. 



Fucus serratus. — This sea-weed also contains a consider- 

 able quantity 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 oc- 

 curs 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 mannite might be more oeconomically procured from 

 this sea-weed than from the usual source, manna. 



