I commented in a post back in March that many algae lived quite happily in an asexual state and that it was rare to see sexual reproduction in “wild” populations. This, in turn, makes it difficult to identify many species (imagine a garden in which the plants only ever produced foliage and never, or rarely, produced flowers). A couple of weeks later I received an email and some photographs from a friend, Chris Carter, who had found some Vaucheria in full “bloom” growing in his garden pond in Northampton. Although it is often bright green in colour, Vaucheria is actually a member of the group of algae called Xanthophyta, and is more closely related to the diatoms than it is to the other green algae. It is another of the annoying filamentous forms that can only be identified to genus in the vegetative state but the presence of sexual organs had allowed Chris to name this population as Vaucheria taylorii.
The vegetative filament (running diagonally from left to right in this image) is a long, hollow tube (about a tenth of a millimetre in diameter in this example) without cross walls dividing it into separate cells. The chloroplasts lie just inside this tube, leaving a large empty vacuole in the middle of the cell. On the outside of the tube there is a rich growth of other algae (mostly diatoms). The sexual organs are on the short lateral branch in the centre of the image. This species is monoecious, meaning that male and female organs grow on the same plant. The oospores, the female reproductive cells, are the dark green ovoid structures growing in a whorl whilst the male organ rises above these and looks, well, male….
The crispness of this image is due to a special technique used by Chris called “stacking”. All microscopists face problems when trying to capture three-dimensional objects because of the low depth of field associated with highly magnified images. “Stacking” involves taking a series of images, adjusting the focus very slightly between each, so that you end up with a series of images of the same object, but each with a different part of the object in crisp focus. Chris then uses a piece of proprietary software to select the sharply-focused parts of each image and combine these into a composite image with apparently greater depth of field than is possible from any single image.
Chris then goes one step further by taking a series of images from two slightly different viewpoints (not as easy as it looks, as the subject has to be tilted slightly between the two sets of images. He then combines each of these to give a composite image, as above, but then he manipulates the image further to remove red from the left image and blue and green from the right image. When the two images are superimposed, the outcome is an “anaglyph”, a stereoscopic image. You’ll need a pair of 3D glasses to see this image properly (the old-fashioned type, with one red and one blue lens). He has made a speciality of this type of photography, producing images of the microscopic world that leap off the page in a dramatic fashion. Of course, like a true artisan, Chris is never happy and commented in a recent email to me that “this seems to be another genus whose 3D characteristics and (messy) environment needs the artist’s brush.” Whereas I, struggling always with brush and paints, look at Chris’ anaglyphs and wish I had his dexterity with a camera. The grass, I guess, is always greener on the other side…