Monday, Sep 22, 2014

Prickly Heat: Why cacti can’t help being thorny

cacti-main The spines are highly modified (trained for combat really), leaves grow out of hairy wooly-looking stubby structures called areolas and which provide the biometric markers of the cacti.
Written by Ranjit Lal | Posted: August 31, 2014 1:00 am

Down In Jungleland

It was as exciting as seeing Halley’s comet, except that this was a flower — an exotic, white, anonymous (to us) cactus flower. It bloomed for one night only — and that was to be that night, sometime between 9 pm and 1 am.

All I remember now was that it kept its date and blossomed waxy white and glowing. I even took a couple of fuzzy black-and-white pictures. It held us in a tragic thrall — imagine, to be so beautiful, for just one night. I looked it up now, maybe 40 years too late. Apparently, it was a member of the Epiphyllum tribe of cacti.

As a rule one stayed away from cacti: anti-social, armed and dangerous. None, by the way, are native to India — they’re New World socialites. But heck, you would be armed and dangerous too, if you lived where it rained for maybe an hour every 500 days and you had to stock up water for the rest. They’re experts at that; a saguaro cactus can apparently tank up 750 litres in the course of a rainstorm. Most of the water is stored in their fat, almost bulbous stems. Most have no leaves and have developed ingenious ways to conserve water.

Photosynthesis, by which magic plants make food out of sunlight and carbon-dioxide, naturally occurs during the day. But in order to take in the CO2, leaves, or in this case, the stems, must open their pores (called stomata) and in doing so, may lose more than 95 per cent of the water the roots have so diligently sucked up in the day. This won’t do in an Atacama scenario. So cacti operate a night shift. The pores in their stems open at night when it’s cool, suck in carbon dioxide, and lose minimal water. The CO2 is stored until the next morning when the sun rises and photosynthesis can proceed. It’s less efficient food-production wise, but you’ll be dead first without water. The spines too serve as windbreaks slowing down evaporation losses and, of course, keep browsers away.

The spines are highly modified (trained for combat really), leaves grow out of hairy wooly-looking stubby structures called areolas and which provide the biometric markers of the cacti. They’re highly modified and compressed shoots and branches, and the flowers too grow from here.

And what flowers they are! When I first visited a cactus show years ago, my jaw dropped: the colours — shocking pinks and magentas, brilliant waxy yellows, blinding whites, crimsons and scarlets — and the petals arranged and engineered to perfection. Squatting smugly like goblets of magical liqueurs or fancy candies on their pincushion thrones of prickles. You may look, you may gasp, you may drool, but you may touch them not!

Cacti belong to the larger continued…

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