Friday fabulous clubmoss

This is a rather poor picture of a very young Selaginella sporophyte (~1.5 mm), the typical and familiar generation of this club moss.  A student has been investigating the use of various common materials for cultivating the haploid generation of free-sporing vascular plants (ferns, clubmosses, horsetails).  It turns out that fine grained terrarium sand sold in pet stores works rather well for this when wet with very dilute liquid fertilizer.  Selaginella has rather smallish and poorly differentiated cones bearing their sporangia at the tips of branches.  The spores come in two flavors, big and little, differing greatly in their ability to disperse and their number.  The big spores become female gametophytes and the little spores become males, which are little more than a sex organ that produces sperm.  This is the same as pollen.  The females stay largely within their spore living primarily on stored food.  The arrow points to the large spore within which resides the female gametophyte that got impregnated and gave rise to this little diploid offspring.  On the grain below the arrow a few little brownish flecks are the little spores that house males.  Some cobwebby rhizoids can be seen above the arrow, outgrows of the female for anchoring, absorbing, and even entrapping small spores so that little males grow in her vicinity.  This part of their life cycle is seldom noticed and when you take pictures with a regular camera through a microscope the depth of field can be rather shallow. 

Growing some haploid ferns

Today's task is to have students start growing some haploid ferns.  Your familiar ferns are diploids and they are asexual producing spores.  Novices often think they have spores but really they have sporangia, which have 128, 256, or 512 spores, there abouts, in them.  They are looking for something small, but they don't realize how small.  If you want to do this yourselves, here's how.  Find a fern with mature sporangia.  The sori, clusters of sporangia, usually look brown at this stage. Take two pieces of white paper.  Fold one into corners and crease it, then flatten the paper back out.  Place the fern frond on the paper sporangia side down.  Cover with the other piece of paper and leave it over night.  As the specimen dries out, the spores are shed onto the paper; look for brownish dust.  The creases make it easy to gather the spores by tapping the paper.  Go to a local garden store and buy a Jiffy 7; they cost about 15 cents.  It's a little compressed pellet of peaty soil in a little mesh bag.  Soak it in water overnight and it will expand.  Get a wide mouth pint canning jar, or an empty peanut butter jar, or something similar.  Turn it upside down and place the Jiffy 7, now more like a Jiffy 42 on the lid to produce a growth chamber terrarium.  Tap spores sparsely onto the surface of the Jiffy 7.  Cover with the jar, screw into the lid and place in a north window.  You don't want direct sunlight, so you also could place it back a ways from a brighter window.  A couple of weeks later you should see green growth.  It's OK to take them out to examine them, and should they need a bit of water place the Jiffy 7 in some shallow water for a few minutes, then return it to its growth chamber.  In 2 months you should have flat haploid ferns about the size of your little finger nail; they are actually called a gametophyte thallus, but it's still a fern, just haploid.  This is the sexual stage of the fern.  A mist of water will cause mature antheridia to release sperm and should a mature egg be around, fertilization will occur and a bit later you'll see the first frond of a diploid fern appear (the familiar phase).  With some patience this can will grow to maturity. 

Plant Porn - Fern Sperm

At the beginning of the semester, one of the 1st things my students do is sow spores of various ferns and lower vascular plants upon a suitable medium. By the time the course gets to vascular plants the gametophytes, especially ferns, are just about mature. One of their instructions is to select one of the mature looking gametophytes, one a bit like this, and mount it in a drop of water
on a slide for observation. What oftens happens the less observant never even notice, but the sharper objects notice something after a few minutes. What are all those jiggly things swimming around? Then slowly comes the thought: sperm! Of course what stimulates a mature gametophyte to release sperm, water, and there you are watching the whole thing. A couple of enterprising students captured a few seconds of this on video. With literally thousands of sperms being released, any mature archegonia would surely get their eggs fertilized. Pretty darned exciting!