Alaria also has a mid-rib at the center of the blade. Both Alaria, Agarum, and Laminaria have a branched holdfast, a stipe and a long flattened blade. They have the same general structure and life cycle as Laminaria described above. _ Alaria and Agarum are kelps that attach in the subtidal and in low intertidal tide pools. As growth proceeds the hole will move towards the tip of the blade and the new tissue can be measured over time. Holes can be punched through the blade above the junction of the blade and stipe with a cork borer. Growth in Laminaria occurs between the blade and the stipe. The gametes, formed by cell division in the gametophyte, join in pairs to form a zygote, which grows into the sporophyte plant. Each zoospore develops into a microscopic, gamete producing a male or female gametophyte. Sporangia on the edges of the blade produce haploid zoospores. The macroscopic plant is the sporophyte stage. In general they have a lifespan of about 4 1/2 years. The tip of the blade often wears away due to the action of waves. (Kelp) has a long flattened blade attached to a thin, rounded, stipe that attaches to the substratum by means of a branched holdfast. As the name suggests it is colonized predominately by large brown algae belonging to the genera Alaria and Laminaria. Sub-tidal Kelp Zone The Sub-tidal Kelp Zone is seldom exposed at low tide and therefore does not experience significant fluctuations in temperature and salinity.
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