Friday, April 06, 2007

mercuries / mallard

Mercurialis perennis (Dog's Mercury or Perennial Mercury)

This is the plant, inconspicuously flowering now, that carpets woodland floors in spring with energetically green leafage. These leaves are in opposite pairs and are ovate-lanceolate, acute, slightly downy on both sides and neatly serrate; successive leaf-pairs are set more or less at right-angles to maximize absorption of the early light in the woods.

M. perennis is dioecious: different clumps of plants are either male or female. In fact these clumps are usually all one plant, though the smaller vertical stems may not produce any flowers. Underneath the ground surface each apparently separate plant is seen to spring from a horizontal white rhizome , several inches long and the same breadth as the vertically ascending stem. Trace the rhizome back to its source and you arrive at the real heart of the matter, a network of tough nodes with strong, cord-like roots.

Dioecious plants are always interesting since the set-up of separate male and female individuals, relatively unusual in the plant world, is the norm for us animals. Plants of both sexes produce their flowers on axillary stems arising above a pair of leaves. The male flower-stems are much longer. One naturally looks for secondary sexual differencebut these are few: while the female plants must sustain fruit until maturity they have far fewer flowers. The essential distinction is about timing; the male effort is now, the female effort comes later. Therefore at this moment the female plants look slightly fresher, neater, healthier, with more rounded leaves and stronger stems. They still hold something back.

Mercurialis annua (Annual Mercury)

This is a scruffy plant, but that may be because its preferred habitat is the dog-tousled verges of urban pathways; it's quite likely not native to the UK and you never seem to find it far from human disturbance. Being an annual, each plant is separate and has its own mop of fibrous roots. The leaves are smaller and less toothed, paler green and nearly hairless; the main stem is branched, producing many more flowers. This species too is dioecious; a surprising arrangement for an annual plant where successful reproduction is so critical, but not all that unusual among wind-pollenated annuals (including cannabis and spinach). Every individual bears flowers; the ones that appear to be non-flowering are females, whose flowers are on very short stems. Since both flowers and leafing side-branches are produced from axils of the main stem, these nodes can be quite crowded, like spaghetti junction. The aerial form of this plant bears an analogy to the undergound parts of the perennial species.

(Mercurialis annua: male plant on the left, female plant on the right. Taken in central Bristol in December.)

Anas platyrhynchos (Mallard or Wild Duck)

Mallards look sweetly peaceful when they pair up at this time of year. In fact their mating behaviour is not always very sweet. I was once watching a duck and drake foraging quietly in a wood when another drake came out of the sky, and forcibly mated the duck while the other drake stood helplessly by. I have also seen a duck incessantly chased by a group of drakes, cornered exhausted between jetties of a reservoir and mounted by each of them in turn.

That was on the water. Also on the water, I saw a drake mount a duck (during mating the duck is almost under water, but for her head which is gripped in the drake's bill). Another drake took exception to this and leaping on the back of the first drake, tried to force his head beneath the surface. Eventually the attacked drake struggled free and fled with the other in brief pursuit, but in the meanwhile the unfortunate duck, three layers deep, was forgotten and its body then re-emerged on the surface, tail and feet up, drowned.

The life of the mallard being so visible to us, humans often witness these scenes and worry about them; to describe them, using words like "gang-rape", "murder", etc. We accept inter-species violence, e.g. of predators on prey, but intra-species violence is more unnerving. Theologically, is there evil in the animal world too? Generally, these outrages occur near the end of the pairing season when most ducks are mated and reclusively nesting. The few remaining ducks in the open are then at risk from a preponderance of unpaired drakes. One looks for the corrupting hand of man in this and it may be that we exacerbate the situation by feeding up the largely-male groups with stale bread in the warmer days of spring, increasing the weight and strength of frustrated males. Besides, these semi-domestic mallards of our parks and urban waterways are often genetically mixed with domestic breeds such as the Barbary Duck grown for extra size, increasing the risk of drowning during aquatic mating. Zoologists will go so far as to surmise that the mallard is an object-lesson in the different, and often conflicting, reproductive motives of the sexes.

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