A. Order Laminariales; Laminaria, Macrocystis and Nerocystis (kelps!
Their large bodies are made up of 3 parts:
*Holdfast (in dark, poorly aerated water) a rootlike mass of tissue that functions, as the name suggests to anchor the stipe in some suitable substrate.
*Stipe-or stem may contain an enlarged air bladders called pneumatocysts
to form flotation blades. These may number up to 100
Other of the stipe cells become reproductive and produce sporangia which
give rise to haploid spores. Sucessful spores form a tiny gametophyte
(hetermorphic generations) which is perennial and may last for 17+ years,
*Blades or the leaf-like extensions are deciduous (annual), During
the time period when the blades have dropped, the algae, must survive
on stored food till new blades form in spring. Some species produce blades
that measure up to 45 m (=130 ft; but are not bulky)
All blades have an:
outer meristoderm that is meristematic(adds new cell layers every year) and photosynthetic
a cortex of parenchyma
central zone of trumpet cells and elongate cellstrue apical meristem which produces true parenchyma tissue
intercalary meristem which produces blades. By intercalary we mean that there exists a region not located at the tip ( which could be eaten or bashed) which has the ability to produce new cells as needed.( This same design is found in grasses, so when you mow the tips, the intercalary meristem below can keep on generating new tissue for you to mow the following week)
