BIOLOGY O F SEAWEEDS O F ECONOMIC IMPORTANCE
147
are well known. Whilst occurring in considerable quantities as freefloating representatives, there are few reports of extensive commercial
exploitation, although numerous species are used as sources of food in
parts of Asia (Chapman, 1950). Studies on the biology of Sargassum
in Japanese waters have also been concerned with the importance of
the free-floating species as nurseries for young fish.
6. Durvillea
Durvillea antarctica plants reach a considerable size (fronds up to
10 m in length), and in many ways they resemble the larger members of
the Laminariales. This alga is a source of food in some parts of South
America, and in New Zealand is used as manure (Chapman, 1950).
7. Macrocystis
The bulk of studies on the biology of these giant kelps have been
carried out on Macrocystis pyrifera (L.) Ag. This work has revolved
around both the seasonal life, reproduction and physiology of the plants,
and in many cases has been aimed at obtaining a more complete
knowledge of full economic potential of the species. The other species
M . integrijolia has been less studied. Womersley (1952, 1954), has
recently described the taxonomy of Macrocystis.
Numerous accounts of the anatomy and morphology of Macrocystis
are available (see summary in Cribb (1954) ) and an account of the more
recent work will be given here. The young sporophyte grows as a
stipitate blade which splits into two equal halves; the secondary blades
so derived then split unequally, and the outer of these last two products
develops a thickened margin at the base on the outer side and this
develops into a stipe which by its elongation separates the many newly
formed blades. Each blade bears a basal pyriform pneumatocyst, so
that the whole stipe then floats along the surface. The terminal blade
continues this splitting process throughout its active life (Fig. 8). Once
the active growth phase is over, deterioration sets in so that the stipe
eventually breaks away from just above the holdfast region. The
number of blades formed wil lvary with the length of the stipe-thus
a stipe of length 250 ern may bear up to sixty blades. The overall
length of the stipe can be appreciably greater than this, and plants of
length 65 ft and over have been described. The holdfast system of
dichotomously branched haptera develops at the same rate as the stipe
and blades, but with age only the outermost haptera survive; hence the
life of the attached plant will depend on the efficiency of the outermost
haptera. However, in most instances a firm anchorage is obtained.
Methods of harvesting Macrocystis fronds have usually been by the
147
are well known. Whilst occurring in considerable quantities as freefloating representatives, there are few reports of extensive commercial
exploitation, although numerous species are used as sources of food in
parts of Asia (Chapman, 1950). Studies on the biology of Sargassum
in Japanese waters have also been concerned with the importance of
the free-floating species as nurseries for young fish.
6. Durvillea
Durvillea antarctica plants reach a considerable size (fronds up to
10 m in length), and in many ways they resemble the larger members of
the Laminariales. This alga is a source of food in some parts of South
America, and in New Zealand is used as manure (Chapman, 1950).
7. Macrocystis
The bulk of studies on the biology of these giant kelps have been
carried out on Macrocystis pyrifera (L.) Ag. This work has revolved
around both the seasonal life, reproduction and physiology of the plants,
and in many cases has been aimed at obtaining a more complete
knowledge of full economic potential of the species. The other species
M . integrijolia has been less studied. Womersley (1952, 1954), has
recently described the taxonomy of Macrocystis.
Numerous accounts of the anatomy and morphology of Macrocystis
are available (see summary in Cribb (1954) ) and an account of the more
recent work will be given here. The young sporophyte grows as a
stipitate blade which splits into two equal halves; the secondary blades
so derived then split unequally, and the outer of these last two products
develops a thickened margin at the base on the outer side and this
develops into a stipe which by its elongation separates the many newly
formed blades. Each blade bears a basal pyriform pneumatocyst, so
that the whole stipe then floats along the surface. The terminal blade
continues this splitting process throughout its active life (Fig. 8). Once
the active growth phase is over, deterioration sets in so that the stipe
eventually breaks away from just above the holdfast region. The
number of blades formed wil lvary with the length of the stipe-thus
a stipe of length 250 ern may bear up to sixty blades. The overall
length of the stipe can be appreciably greater than this, and plants of
length 65 ft and over have been described. The holdfast system of
dichotomously branched haptera develops at the same rate as the stipe
and blades, but with age only the outermost haptera survive; hence the
life of the attached plant will depend on the efficiency of the outermost
haptera. However, in most instances a firm anchorage is obtained.
Methods of harvesting Macrocystis fronds have usually been by the