MadSci Network: Botany


Date: Mon Apr 16 21:45:20 2001
Posted By: Evelyn Tsang, Research Assistant
Area of science: Botany
ID: 981821033.Bt

Hello Andy!

Sorry to take so long in answering your question!  :}

A plant grows when new cells are produced, and there are localized regions 
within a plant for cell production.  These areas are called the 
meristems.  The most easily noticed meristem is the shoot apical 
meristem on plants; it is the tip of the plant stem.  The apical meristem 
looks like a cap, with new cells dividing underneath it and pushing it 
forward (or in this case, upwards).  There is another apical meristem on 
the tip of each root.  There are also lateral meristems found in a bud(s) at 
each node along the stem. There are chemicals, auxins, that the apical meristem 
produces which prevent the lateral buds from growing. When you prune a flower 
bush, you are chopping off the apical meristems so that the lateral buds
start to grow out and you end up with a many-flowered bush.

As for algae they are not considered plants - they have their own 
taxonomic division as Protists. There are six different subgroups (phyla) 
of algae.  Three of these six phyla are single-celled organisms, so they 
would produce more algae simply by dividing. 

Red, brown and some green algae are also known as seaweeds.  

These are multicellular organisms that actually form plant-like structures 
but they are not as complex as the stem, roots and leaves of real plants.  
For instance, green algae can form large structures (like sea lettuce) but 
the cells found in any part of the organism are pretty much all alike 
instead of being differentiated into stem, roots, etc.  Algal growth is in 
the form of a filament either with new cells developing from the end of 
the last cell in the filament, or with cells dividing between two other 
cells within a filament. The most complex algae are the brown algae (the 
kelps).  These actually have differentiated cells to transport material 
internally and some kelps actually have a meristem-like growth area but 
again, the structures that an algae develop are not as complex as that 
found in plants.

Thanks for waiting for my answer!


Sites of interest:

Algae photos

Drawing and photos to describe a plant meristem: http://ww

Text references:  

An Evolutionary Survey of fungi, algae and plants.  J.C.Semple & 
B.Kendrick, Dept of Biology, University of Waterloo. 1992.

Life.  R.Lewis, Wm.C. Brown Publishers, Dubuque, IA. 1992.

David Hershey adds:

Woody plants have a vascular cambium, which lies underneath the bark and is 
responsible for the increase in stem and root diameter. 

Grass plants have an intercalary meristem at the base of each leaf which allows 
the leaf to regrow after mowing, even though the leaf tip has been removed. It 
operates differently than an apical meristem. An intercalary meristem is more 
like squeezing toothpaste out of tube because growth occurs at the base. With 
an apical meristem, it is more like stacking blocks because growth occurs just 
behind the tip.

Kelps (a type of algae) and bulbs, such as daffodils and onions, also have 
intercalary meristems at the base of their leaves.


Grass Structures - Mechanisms for Growth


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