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About "Ask A Scientist!"

On September 17th, 1998 the Ithaca Journal ran its first "Ask A Scientist!" article in which Professor Neil Ashcroft , who was then the director of CCMR, answered the question "What is Jupiter made of?" Since then, we have received over 1,000 questions from students and adults from all over the world. Select questions are answered weekly and published in the Ithaca Journal and on our web site. "Ask A Scientist!" reaches more than 21,000 Central New York residents through the Ithaca Journal and countless others around the world throught the "Ask a Scientist!" web site.

Across disciplines and across the state, from Nobel Prize winning scientist David Lee to notable science education advocate Bill Nye, researchers and scientists have been called on to respond to these questions. For more than seven years, kids - and a few adults - have been submitting their queries to find out the answer to life's everyday questions.

Previous Week's Question Published: 28 May, 2008 Next Week's Question
Do leaves grow back in the same place every year?
Question
Do trees have leaf "pores" where the leaves grow back every year in the same place, or do leaves grow back in different spots along a branch?

Question
While trees do have extremely small pores on their stem and leaves. this is not where new leaves arise. At the tip of every stem, either a larger main stem, smaller side stems, or even the just above every leaf stalk lies a special stem tip, called a stem apex, that takes the form of a bud. If we cut across the tip of this bud it consists of a dome that is, or can, form new tissue, so growing in length. On the edges of this dome little side-domes form that, as they grow, develop into the leaves. In spring the stem tip starts growing, the outer scales of the bud open up, and the leaves expand, as you can see in the accompanying photos. The leaves always arise at a different point every year, even though, on some slow-growing side buds, this may be close to the previous year's position.

Pores (called stomata) on the leaves, which are too small to see with the naked eye, enable carbon dioxide to enter the leaves, where it is used to make sugars by the process of photosynthesis. These pores also allow water vapor to escape (a process referred to as transpiration) so that plants need a continual water supply. Woody twigs also contain pores called lenticels, which look like brown dots on the surface of the young twigs. These enable oxygen to get into the inner tissues for respiration.

Tiny spores, or stomata, in the surface layer of a leaf (magnified about 1000 times).

A vertical section through a bud (yes, it's a Boston lettuce!)

This series of photos (left to right, top to bottom) shows the buds at the tip of a branch of a Horse Chesnut tree (Aesculius hippocastanum) as they open in spring.