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.
Tuesday, March 31, 2009
Monday, March 30, 2009
The leaves of the oleaster (Elaeagnus sp.) shrubs in my garden are glossy green above and dazzling white below. The cause of the highly reflective undersurface is revealed under the microscope – thousands of overlapping, flattened hairs, shaped like multi-armed starfish. Each is about a fifth of a millimetre in diameter and attached to the leaf surface by a short stalk. Imagine a surface covered in vast numbers of overlapping, flat, open umbrellas and you’ll have a pretty accurate mental picture of how they’re arranged. The hairs prevent excess water loss from the pores (stomata) on the leaf undersurface, while allowing free passage to the all-important carbon dioxide that the leaf needs for photosynthesis.
Friday, March 27, 2009
Three more photos taken with the USB microscope. The top image is of the Marchantia polymorpha liverwort that grows on the surface of overwatered plants in my greenhouse. The objects in the centre of the cupule are tiny buds called gemmae, miniature liverworts that will begin to grow when they are splashed out onto the soil surface by the spray from the watering can. You can also see the air pores in the surface of the liverwort thallus quite nicely. The other two images are of a lesser celandine and a dandelion. One minor problem with this USB microscope is that the images can be a bit flat, especially if the objects are predominantly one colour, as the ring of LEDs that provides the illumination produces shadowless lighting.
Here are some pictures taken with my new toy, a borrowed Dinolite USB microscope. It plugs into the USB port on a laptop and has a ring of LEDs around the lens to illuminate the subject, plus a knurled focussing wheel – and that’s it. You take a picture by clicking F11 on the keyboard or by gently tapping a sensitive point on the instrument. It will take a bit of practice to become proficient but so far I’m quite pleased with what it’s delivering. This would be a useful instrument for a naturalist and would be ideal for showing your kids the miracles of the microscopic world, especially if the laptop is coupled to a digital projector, so that the images are projected onto a large screen. Next step is to borrow a netbook and see if I can run it off that, in which case it might make low-power microscopy in the field a feasible proposition. The (not very exciting) pictures are of a very young woodlouse (length about 3mm.), and groundsel flowers. On the case of the flowers, you can easily count the pollen grains at the highest magnification. The woodlouse in the picture is the common pigmy woodlouse Trichoniscus pusillus, that normally lives in woodlands but thrives in the pine bark mulch I've used in my garden.
Sunday, March 22, 2009
Mosses reproduce by shedding wind-dispersed spores from capsules carried on slender stalks. Different species use different methods for regulating the replease of spores. This one - Catherine's moss Atrichum undulatum - has a series of slits around the mouth of the capsule and shakes spores out like pepper from a pepper pot, as the capsule stalk vibrtaes in the wind.
Saturday, March 21, 2009
These are juvenile flat periwinkles (Littorina obtusata) developing in a blob of jelly on the surface of a seaweed. Each animal, developing inside its translucent, delicate, helical shell, is about half a millimetre in diameter at this stage. When it hatches from the jelly this marine snail will eventually reach a diameter of about one and half centimetres.
This is a rotifer - a tiny aquatic animal about one tenth of a millmetre long. Twenty, placed end to end, would stretch across the head of a dressmaker's pin. Rotifers feed by using two circles of rhythmically beating cilia ('wheel organs') on their head, which create a vortex that sweeps food particles into their digestive tract, into the path of constantly grinding jaws called the mastax, which you can see below the wheel organs. The animal attaches itself with a tail and, in some species, when it lets go of its anchorage the wheel organs can become propellers. Rotifers are every where where there is water - in puddles, in wet mosses and even in a vase of flowers that has been standing on the windowsill for a few days - which is where this one came from.