Why do some plants have prickles?
  • Plants have prickles for protection from animals who may like to eat them and from humans that may like to pick them.
  • Plants like cacti have prickles instead of leaves because leaves release a lot of water and cacti living in the desert canít afford to lose too much water.
  • Leaves have tiny little holes called stomata on their undersides that let gases pass in and out of the leaves. Those holes also release tiny particles of water. The bigger the leaf the more water is released.
  • So plants like cacti have tiny thin prickles instead of leaves because the prickles will release far less water than a big flat leaf.
  • Cacti also use their prickles to protect themselves from desert animals that would love to chew on their juicy flesh.
  Did You Know?
  • Prickly plants like gorse and thistles were brought into New Zealand with the first settlers.
  • Gorse was planted to make a prickly hedge that animals wouldnít eat or get through
  • Some seeds have prickly barbs on them that hook onto the fur/wool of animals so the seeds get to travel - get distributed.
Test Transpiration

Very carefully tie a plastic bag around several leaves on a plant. Check the plastic bag a few hours later and youíll probably notice condensation forming on the inside of the bag. This is the water that has been released by the leaves in the plastic bag. Try the experiment on a cold day and then on a hot day; on a big leaf and a small leaf and on hard and soft leaves of the same size. Does it make a difference to the amount of water that has been transpired (thatís what itís called)?
How many different plants can you name with prickles. Why do they have prickles - what are they protecting themselves from? What tree has spiky prickly leaves and has a special job in the summer holidays - why does it have thin prickly leaves instead of big flat ones?
Whatís a prickles favourite food?
Prickled onions
From Jessica

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