Marsilea
- Cloverleaf fern: Family Marsileaceae - Pepperwort Family
Observation
of Heterogamy and Alternation of Generations
A
B 
C 
D 
E
F
G 
-
A.
Sporophyte generation produces sporocarps that develop from the base of
a runner during late spring or early summer. The sori within the sporocarp
encase two different types of gametes. The development
of two different types of gametes is known as heterogamy.
-
B.
A dried sporocarp is scarcified (scraped) and
put in spring water. Two types of cells can be seen as the sporocarp
swells. Macrospores which develop into female gametophytes.
Microspores which develop corkswcrew-shaped, multi-flagellated sperm within
the spore.
-
C.
Immature macrospore about 2 hours into activation. The gametophyte
develops internally but the neck of the archegonium protrudes.
-
D.
Microspores open about 7-8 hours into development. The microspores
divide many times to form a ball of cells, some of which will become sperm.
With luck you will see the spinning flagellated sperm.
-
E. The developing
female releases a gel like mass to trap and guide the sperm up the neck
of the archegonium. This image was taken 8 hours into development.
The sperm have been released and are motile. The egg is ready for
fertilization.
-
F. Within 40
hours an embryonic sporophyte emerges from
the female gametophyte. Alternation from a gametophyte to a sporophyte
generation has occured.
Terms to be familiar
with:
alternation of generations
sporophyte - diploid
gametophyte - haploid
macrospore
microspore
heterogamy
Be able to diagram a general life cyle
of a fern.
Additional
Developmental Information
Sporocarp Source:
Carolina Biological Supply
Company
Catalog # K 3-15-6932
Marsilea Sporocarps
They also sell live marsilea
ferns.
Image credits:
All images were taken by
Nancy Hein, Hawley High School, Hawley, TX. with a Sony Mavica Camera
or video captured through a microscope with a VideoBlaster card or SnappyCam.
October 1998