Friday, 14 February 2014

Transpiration and water conservation by plants

Dying to go
A large oak tree can breathe out 150 gallons of water in a day
      Maybe it's only me, but I find it easy to build a seemingly minor situation into a major catastrophe in my own mind:

      We went to a play called 'Pride' the other night. Usually our theatre trips are confined to the cheaper seats entailing the use of binoculars and, on occasion, vertigo tablets. There are numerous actors whose faces are unknown to me. Show me the top of their heads though, and I know them like a family member. In the Royal Shakespeare Theatre, Stratford, I needed Superman x-ray vision to see round a roof support. However, for 'Pride', my wife had got us possibly the best seats in the house - second row from the front and slap bang in the middle.

      The play was a well-acted study of the unbearable stress a judgemental society places on someone who happens to be gay - people marrying members of the opposite sex to prove to themselves and others that they are 'normal' and in the process messing up both their own and their partner's lives. An insecure, angst- ridden gay relationship inevitably ensues and the play is making a powerful point.

      Unfortunately, within ten minutes of the start, I needed to go for a pee. The fact that I was in the middle of the row however meant that whichever way I went I'd be disturbing about twelve people in full view of the rest of the audience. So I gritted my teeth and determined to stick it out until the interval, using the usual stratagems of shaking my legs and breathing deeply. When I say 'usual stratagems', they may not be yours but are most certainly mine, although I don't know whether a scientific basis has been established. Certainly it is widely recognised that not thinking about liquid helps, and the fact that virtually every scene involved someone pouring drinks was tantamount to tap-dancing on my bladder.

      Anyway, the gay relationship on stage was going through the doldrums and one bloke was threatening to leave. I was pinning my hopes on the likelihood that him leaving the stage would coincide with the interval and I would be able to find relief. A couple of times he walked to the door and was about to go, then he'd come back to continue arguing and I got to the stage where my mind was screaming for the bugger to sod off. Then a horrible thought struck me: very occasionally there isn't a break - the play runs straight through to the end. Christ! my bladder would burst. By weighing up the alternatives of the audience being slightly disturbed against that of them getting their feet wet, I came to a momentous decision, got up and excused myself  to each and every person as I tripped over their hand bags and trod on their feet.

      Eventually I reached the end of the row, aware that a highly dramatic point had been reached on stage, with long silences only broken by this manic prancing figure bobbing along in front, crashing through people's personal accoutrements. Half expecting some comment from the stage along the lines of  'was it something I said?' I reached the exit door. Well- lit by the overhead sign, it was covered with a curtain which I wrestled with, trying to pull it in the wrong direction while, ridiculously, feeling that that everyone in the place was watching me: I'd got myself my own little stage and should give a bow before finally exiting. Old time comics; Charlie Chaplin or Laurel and Hardy, would get a half-hour sketch out of this performance.Then I conquered the curtain and was free, rushing up the stairs to the gents and knowing that I hadn't got the nerve to do this process in reverse - I'd wait until the break before I went back in and, if there wasn't one, I'd just lurk somewhere. It crossed my mind that, in case (God forbid!) this scenario was to repeat itself some time in the future, I'd carry a false moustache, and maybe a wig, in order to escape recognition on leaving the gents.

      I was standing at the urinal, enjoying well earned moments of bliss, when the door burst open and a number of blokes rushed in. At first I thought they'd come to get me but quickly realised that it was the break. I'd left about thirty seconds too soon. That man had left the stage at last.

      And, while plants don't actually cross their legs at the theatre, they still lose a hell of a lot of water (around 90% of intake) through their leaves in a process called transpiration. A large oak can transpire 150 gallons of water a day, which is why pools in woodland area are there all winter but, as soon as the trees sprout leaves, many completely dry up. This is the reason  that we put a plastic bag over cuttings: creating a densely humid atmosphere around the leaf slows down transpiration because water molecules find it difficult to bludgeon their way out. In this way water stays in the cutting until such time as it grows roots capable of replacing water loss.
Cactus spines do more than just deter predators
      At one time, houseplants were much happier in the environment of the living room. That was because we all had coal fires and the burning coal needed oxygen to keep it going, so it sucked fresh air in wherever it could: around window frames, under the door and so on. The thing was, that air contained moisture, something lacking in today's radiator- warmed rooms with their inherent dryness. Not many plants thrive in completely dry air, so we can rectify this by standing them on saucers of grit which is kept damp. The grit provides a large surface area for water to evaporate from, rising to provide a moist microclimate around the leaves and slowing transpiration. Take care not to have the plants standing in water though, as this can lead to lack of oxygen in the compost.

      Plants in very dry situations adapt to slow down water loss in a number of different ways:
Heather moors - Ericas  have evolved their own 'plastic bag' for retaining water
      Heath (Erica) has leaves which curl in on themselves so that they look like a horse-shoe in cross-section. The pores (stomata) are on the underside of the leaf, inside the horse-shoe and are surrounded by hairs. The effect of this is to create a moist microclimate which works in the same way as the plastic bag over our cuttings, slowing water loss; some plants, like Brachyglottis greyii, cover the surface of the leaf with silver hairs which not only slow drying wind movement but reflect the sunlight and reduce water loss  due to overheating. A surprising number of common plants use this technique but it often needs close examination for the hairs to become apparent; cacti, renowned for coping with very dry conditions, have spines performing the treble tasks of deterring browsers, trapping moist air near the surface and acting as a point for mist to condense and run down to the roots. Many cacti are ribbed and the ribs disappear when the plant expands with stored water, only to reappear as it is used up; silvery leaved plants, like lavender, reflect the sun's rays in the same way as those with hairs and this characteristic is something to look out for when choosing plants for a dry spot.

      So it can be seen, just from the few examples I've shown, that plants are far better than me at retaining water.

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