BIOLOGY O F SEAWEEDS OF ECONOMIC IMPORTANCE
149
harvesting. This is possible because of the extensive growth observed,
and the ability of the plant to replace the lost surface canopy (Clendenning, 1964). There can also be a prolific growth of new frondage
from the holdfast region, these new branches growing upwards as
bundles of stipes entwined together in a helical pattern, and so able to
withstand the buffeting of the sea despite their slender nature. Intercalary growth enables extension growth of the stipe, and the activity
of a primary meristem at the blade tip acts as a source of new blades.
In deeper water the internode lengths show a considerable increase in
length. It has been stated that young fronds growing from the holdfast
region are unable to maintain an adequate rate of growth by their own
assimilation, and that some of the assimilatory products of the surface
blades are translocated in the medulla. Evidence for this has been
obtained by observing the effect on growth of the young fronds of
exfoliation of the blades near the surface ; more conclusive evidence
would be obtained by use of radioactive compounds (Sargent and Lantrip, 1952; Clendenning, 1964). Metabolic activity is at a fairly high
rate in blades with a high percentage of meristoderm, and a marked
gradient of activity is to be observed. A t the apex of the frond the
activity is relatively low in the young fronds, and at a maximum
between the 80 to 100th blade from the tip. Thence the rate falls off
with increasing senescence of the blades near the base.
Assimilatory activity in a giant kelp frond has been likened to an
advancing wave, with the " crest " 2-3 m back from the frond tip (Clendenning, 1964).
In California the average frond life is estimated to be 4-7 months,
although North (1961) found that some fronds survived only 2-3
months, and with growth in deeper water lengths of 100 ft can be
reached in the course of a year. A rapid regeneration of new frondage
after harvesting has been observed, and growth rates of up to 18 in
per day have been recorded. Observations on the rates of growth of
Macrocystis in Tasmania were made by Cribb (1954). In sheltered
fringing beds the age of the stipes was estimated to be between 7-10
months, and new blade production occurred on approximately every
2nd day. Rapid elongation of the stipe may be seen in the larger
number of blades being initiated in the apical 5-10 cm. Detached
apices with stipes 50 cm or more continued to produce new blades,
although shorter lengths of stipe failed to do so. Removal of the
terminal blade inhibited continued growth of newly initiated blades.
The bulk of the meristematic activity of the blade is in the basal
region immediately above the pneumatocyst. Some 2-3 months elapse
between blade initiation and maturity. With advancing age the apical
149
harvesting. This is possible because of the extensive growth observed,
and the ability of the plant to replace the lost surface canopy (Clendenning, 1964). There can also be a prolific growth of new frondage
from the holdfast region, these new branches growing upwards as
bundles of stipes entwined together in a helical pattern, and so able to
withstand the buffeting of the sea despite their slender nature. Intercalary growth enables extension growth of the stipe, and the activity
of a primary meristem at the blade tip acts as a source of new blades.
In deeper water the internode lengths show a considerable increase in
length. It has been stated that young fronds growing from the holdfast
region are unable to maintain an adequate rate of growth by their own
assimilation, and that some of the assimilatory products of the surface
blades are translocated in the medulla. Evidence for this has been
obtained by observing the effect on growth of the young fronds of
exfoliation of the blades near the surface ; more conclusive evidence
would be obtained by use of radioactive compounds (Sargent and Lantrip, 1952; Clendenning, 1964). Metabolic activity is at a fairly high
rate in blades with a high percentage of meristoderm, and a marked
gradient of activity is to be observed. A t the apex of the frond the
activity is relatively low in the young fronds, and at a maximum
between the 80 to 100th blade from the tip. Thence the rate falls off
with increasing senescence of the blades near the base.
Assimilatory activity in a giant kelp frond has been likened to an
advancing wave, with the " crest " 2-3 m back from the frond tip (Clendenning, 1964).
In California the average frond life is estimated to be 4-7 months,
although North (1961) found that some fronds survived only 2-3
months, and with growth in deeper water lengths of 100 ft can be
reached in the course of a year. A rapid regeneration of new frondage
after harvesting has been observed, and growth rates of up to 18 in
per day have been recorded. Observations on the rates of growth of
Macrocystis in Tasmania were made by Cribb (1954). In sheltered
fringing beds the age of the stipes was estimated to be between 7-10
months, and new blade production occurred on approximately every
2nd day. Rapid elongation of the stipe may be seen in the larger
number of blades being initiated in the apical 5-10 cm. Detached
apices with stipes 50 cm or more continued to produce new blades,
although shorter lengths of stipe failed to do so. Removal of the
terminal blade inhibited continued growth of newly initiated blades.
The bulk of the meristematic activity of the blade is in the basal
region immediately above the pneumatocyst. Some 2-3 months elapse
between blade initiation and maturity. With advancing age the apical