EEB340 Lecture 16.docx

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12 Apr 2012

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Lecture 16: Alternation of Generations
Alternation of Generations
Ferns (leptosporangiate)
Leptosporangiate Ferns
- sorus is an aggregation of sporangia
- come sori are convered by an indusium covering over the sporangium protects
the sporangia
- indusium dries and shrivels so mature spores better able to be dispersed into the
- diversity in how sori are arranged on the sporophyll
- different modes of maturation of the sporangia some allow for gradual
maturation so that spores may be produced over longer period of time
- sori may be sitting on leaf margin
- false indusium: leaf margin curling to protect the sporangia
- annulus is the function equivalent of the endothecium
o cell wall thickenings help them bend back when dry
o stomium is a small cell and area of weakness that allows for splitting of
sporangium endothecium
- fern gametophytes are variable in morphology
- these ferns are heterosporous
Water Ferns
- water ferns are also heterosporous
- sporocarp: highly reducted leaf, functionally a sporophyll
- sporocarps develop in assocation with the megaphylls
- Marsilea 4 leaf clover water shamrock
- The sporocarp is heavily scalarified
- The sorophore is the lower layers of the sporocarp cell walls have tons of pectin
in them; cells swell with water once sporocarp has imbibed water
- Sorophore is where sori develop
- Each sorus develops a megasporangium and 2 microsporangia
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