IN ONE of Shakespeare's lesser plays, The Famous History of the Life of King Henry VHI, Queen Katherine, understandably, is peeved around the middle of Act III. "Take thy lute, wench," she snaps at one of her ladies gathered round: "My soul grows sad with troubles; sing and disperse em if thou canst." And the girl obliges with a little ditty that begins:
Orpheus, with his lute, made trees
And the mountain tops that freeze,
Bow themselves when he did sing.
Now, trees on mountain tops that freeze have more important matters to contend with than paying homage to a busking Greek. Very low temperatures affect plant life in much the same way as icy conditions cause problems with domestic plumbing water expands as it freezes, and as it does so it is liable to shatter the cells of plants containing it, just as water turned to ice may burst domestic pipes. Trees and other plants survive the cold because they have developed very clever tricks for doing so.
Many trees, for examples, adopt an attic strategy: they provide themselves with lagging jackets in the form of thick and craggy bark, whose insulating properties protect them from the worst effects of falling temperatures. Some plants, on the other hand, have what we might call a motoring solution: they add an antifreeze to their hydraulic systems in the form of salts, sugars or other chemicals that lower the freezing point of their internal fluid.
Yet others exploit the fact that water finds it difficult to lapse into the solid state unless it contains specks of impurities on which the ice can grow; some plants maintain their water "supercooled" as a liquid well below the nominal freezing point by insuring their internal plumbing is kept scrupulously clean.
Another way of coping with the ice is to avoid the problem altogether. Annual plants just fade away and die, and leave the problem of survival to their seeds. The seeds themselves are dehydrated, so there is no water to expand and damage them, and they can survive for months or years or even centuries, until charged with moisture and triggered into growth by rising temperatures.
The rhododendron has managed to adopt this strategy while staying alive. It uses a "freeze dry" technique, whereby as the temperature falls with the approach of winter, the sap inside the plant is siphoned out, leaving dehydrated tissues that can survive the very coldest of conditions; the following spring, water is pumped back into the leaves, and growth resumes.