The Magic of Mushrooms

These are the radiating gills of the toadstool known as weeping widow Lacrymaria velutina. For more about this toadstool, visit http://cabinetofcuriosities-greenfingers.blogspot.com/2009/10/weeping-widow.html

The surface layer of the gills, known as the hymenium, produces thousands of spores, and for these to be successfully released into the airstream the gills must always be vertically aligned, so they are very sensitive to the force of gravity and quickly realign themselves if the stipe of the toadstool bends away from the vertical and tilts the cap.

Here, at a microscope magnification of x40 you can see the spores lining the surface of the gills....

...and here, at a magnification of x100 you can see that each is shaped like a small brownish-black lemon..

The spores are formed in groups of 4 on a cell called a basidium, attached to it by short stalks, seen here at a magnification of x400 under the microscope....

... and these appear to be two basidia where the spores are beginning to form. When they're mature and drop off they'll fall vertically down the gaps between those parallel, perfectly vertical gills and will be wafted away in the airstream

If you cut off a toadstool cap, turn it gill side down on a piece of paper of contrasting colour to the spores and leave it in a warm room where there are no draughts for a couple of hours, the falling spores will produce a beautiful spore print.....

...like this

Nature’s Siege Catapults

Turn over a fern frond at this time of year and you’ll find that the underside is covered in rows of what look like small blisters (bottom photo). These are scores of spore- producing structures called sporangia, clustered together under a membrane that keeps them moist while they’re developing. In the example illustrated here the membrane is kidney-shaped, which is characteristic of a buckler ferns in the genus Dryopteris. Once the spores in the sporangia are ripe the protective membrane withers and at this stage the sporangia – sometimes more than a hundred in each cluster – look like minute black eggs when you look at them with a hand lens (second and third pictures from bottom - double-click any image for an enlarged view). Each individual sporangium is a minute catapult that fires its spores out into the airstream. You need to look at a sporangium under a microscope to see its detailed structure and decipher how it works (top photo). Each sporangium, mounted in a stalk and stuffed full of spores, is egg-shaped and has a 'spinal column' of thick-walled cells (showing up in vivid colours in these polarised light micrographs) stretching about two thirds of the way around its vertical circumference. Once these cells are exposed to air they lose water through their thin outer wall that you can see in the second photograph from the top, drawing this outer wall inwards via the surface tension of the remaining water inside. This creates tension inside each cell and, repeated all the way along that ‘spinal column’ of cells, draws the 'spinal column' back like a bowstring, ripping open the sporangium and exposing the spores inside. Eventually the remaining water in each cell in the 'spinal colum', under immense surface tension, vapourises instantaneously and the natural springiness of the thick walls of the sporangium flicks the spine back to its original position, hurling out the spores like rocks from a Roman siege catapult. Once the spores - each around a hundredth of a millimetre in diameter - reach the airstream they can be carried vast distances. Ferns are often amongst the first plants to establish themselves on new volcanic islands and lava flows, thanks to their spores' incredible aerial mobility, which also allows them to colonise unlikely places in urban environments. Next time you're walking through any city, look up at the gutters and you'll see ferns growing that arrived as wind-blown spores. What happens next, after a spore lands and germinates, is an equally remarkable tale of frantic sexual reproduction .... but that’s another story.

Aerial invasion

These are the fertile shoots of the notoriously invasive field horsetail Equisetum arvense, produced in spring a couple of weeks before the green photosynthetic shoots appear. When it dries out the spear-shaped point of each fertile shoot breaks up into stalked, polygonal structures with spore sacs underneath. When the spores are first released they have four arms, called elaters, with club-shaped ends wrapped tightly around the spore. The elaters immediately unwrap themselves in the dry air and assume the shape of a cross, increasing the surface area and aerial buoyancy of the spores so that they can be carried miles in the breeze.....and infest another garden. Each spore is about one twentieth of a millimetre in diameter. The short video sequence below shows the almost explosive release of tension in the elaters when they uncurl in the first few seconds after release into dry air.