BIOLOGY O F SEAWEEDS O F ECONOMIC IMPORTANCE
207
mannitol contents were about 2% higher in plants growing in habitats
exposed to severe wave action. A comparative study was also made of
the chemical composition of the receptacles and sterile apices of plants
from the three contrasting habitats. Whilst the receptacle composition
varied little with habitat, the sterile tips showed a similar variation
to that described above for the larger fronds. When a seasonal analysis
was made of receptacles and sterile branches marked differences were
observed. Thus the mannitol content of the sterile tissues was low in
December, but steadily increased through spring and summer ; by
contrast the mannitol in the receptacles was highest in December and
thence fell progressively ; but the minimum content of the sterile fronds
was higher than the winter maximum of the receptacles. Similarly
the alginic acid content of the sterile tissue was appreciably higher than
that of the receptacles in winter, and in both cases the quantities fell
progressively, reaching a very low value in the case of the receptacles.
Here again, the maximum value observed in the receptacles was lower
than the minimum value of the sterile tips. These lower values in receptacle tissue were also seen in dry weights, total ash and crude protein.
The observations recorded above are of some significance, since the
fruiting tissue makes up a considerable proportion of fertile plants
(estimated at half the fresh weight), and the fruiting plants will clearly
be of lower value on harvesting.
Whilst Himanthalia elongata is of little economic value, the unusual
form of the plant with the cup-shaped frond and the strap-like receptacles enables a more critical analysis to be made of sterile and fertile
tissues (Moss, 1952b). Thus the mannitol content of the sterile tissue
falls with growth of the thongs, 'and the laminarin content was low in
both tissues. Whilst the developing fronds show steady increases in
mannitol, crude protein and alginic acid, the young thongs have higher
protein and alginic acid contents than the fronds which produce them.
These results further demonstrate the differences in extractive content
of fruiting and sterile tissues.
Macpherson and Young (1952) reported the seasonal variation in
chemical composition of fucoid algae from the Maritime Provinces of
Canada (Pucus vesiculosus, P. evanescens, Ascophyllum nodosum). Of
the principal extractives, mannitol was highest in summer and autumn,
whilst the laminarin changed little over the course of the year. Alginic
acid was a t a maximum in the winter, falling in spring and summer ; the
total ash content was the converse of this.
Black and Dewar (1949) made a detailed investigation of the more
significant physical and chemical properties of the sea, and attempted
to correlate these observations with the annual changes in the chemical
207
mannitol contents were about 2% higher in plants growing in habitats
exposed to severe wave action. A comparative study was also made of
the chemical composition of the receptacles and sterile apices of plants
from the three contrasting habitats. Whilst the receptacle composition
varied little with habitat, the sterile tips showed a similar variation
to that described above for the larger fronds. When a seasonal analysis
was made of receptacles and sterile branches marked differences were
observed. Thus the mannitol content of the sterile tissues was low in
December, but steadily increased through spring and summer ; by
contrast the mannitol in the receptacles was highest in December and
thence fell progressively ; but the minimum content of the sterile fronds
was higher than the winter maximum of the receptacles. Similarly
the alginic acid content of the sterile tissue was appreciably higher than
that of the receptacles in winter, and in both cases the quantities fell
progressively, reaching a very low value in the case of the receptacles.
Here again, the maximum value observed in the receptacles was lower
than the minimum value of the sterile tips. These lower values in receptacle tissue were also seen in dry weights, total ash and crude protein.
The observations recorded above are of some significance, since the
fruiting tissue makes up a considerable proportion of fertile plants
(estimated at half the fresh weight), and the fruiting plants will clearly
be of lower value on harvesting.
Whilst Himanthalia elongata is of little economic value, the unusual
form of the plant with the cup-shaped frond and the strap-like receptacles enables a more critical analysis to be made of sterile and fertile
tissues (Moss, 1952b). Thus the mannitol content of the sterile tissue
falls with growth of the thongs, 'and the laminarin content was low in
both tissues. Whilst the developing fronds show steady increases in
mannitol, crude protein and alginic acid, the young thongs have higher
protein and alginic acid contents than the fronds which produce them.
These results further demonstrate the differences in extractive content
of fruiting and sterile tissues.
Macpherson and Young (1952) reported the seasonal variation in
chemical composition of fucoid algae from the Maritime Provinces of
Canada (Pucus vesiculosus, P. evanescens, Ascophyllum nodosum). Of
the principal extractives, mannitol was highest in summer and autumn,
whilst the laminarin changed little over the course of the year. Alginic
acid was a t a maximum in the winter, falling in spring and summer ; the
total ash content was the converse of this.
Black and Dewar (1949) made a detailed investigation of the more
significant physical and chemical properties of the sea, and attempted
to correlate these observations with the annual changes in the chemical