with big sharp pointy ...leaves

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Leaves With Pointy Edges Explained

By Jennifer Viegas, Discovery News

 

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Feb. 17, 2006 -Leaves either have smooth or pointy, " toothed " edges,

and now researchers think they know why - the teeth take some of the

bite out of cold weather for trees, shrubs and other plants.

 

Since the study, published in the current International Journal of

Plant Sciences, links leaf teeth to climate, the finding suggests

analysis of leaves from ancient and existing plant species could reveal

past and present climactic patterns.

 

These are critical for determining periods of global warming and other

profound temperature changes.

 

Dana Royer, who authored the study with Peter Wilf, told Discovery News

that the jagged, pointy edges on leaves are packed with a tissue called

xylem that transports sap, which contains water and nutrients. Most of

the liquid evaporates by leaving the teeth through minuscule pores.

 

" In the springtime when leaves are just starting to leaf out, leaves

with teeth are, on average, losing more water than leaves without

teeth, " said Royer, an assistant professor of earth and environmental

sciences at Wesleyan University.

 

" This loss of water helps pull more sap up from the roots. Thus trees

with toothed leaves probably have a higher rate of sap flow early in

the spring than toothless leaves. "

 

He added, " This is important because it delivers nutrients to the

developing leaves, helping to 'jumpstart' their photosynthetic season.

As you move to colder and colder climates with shorter and shorter

growing seasons, it becomes increasingly beneficial to have teeth. "

 

The researchers measured such moisture evaporation, called

transpiration, and photosynthesis activity for leaves on 60 woody

species from two regions with differing climates: Pennsylvania and

North Carolina.

 

They determined that both energy-gathering activity and transpiration

increased at jagged leaf edges by up to 45 percent during the first 30

days of the spring growing season. Leaves without teeth did not exhibit

such a marked increase.

 

The scientists also found that plants native to colder climates, like

those in Pennsylvania's south central York County, had toothy edges

that were especially active.

 

Possessing teeth may not always be advantageous for leaves, however,

since the teeth also promote more water loss. Plants in dryer regions

seem to be better off if they have fewer teeth or are toothless.

 

Another theory, proposed by Taylor Field at Taylor University, holds

that leaf teeth serve as a sort of " release valve " that prevents too

much sap from collecting in the leaf.

 

Judith Totman Parrish, dean of the College of Science at the University

of Idaho, told Discovery News that she thinks the jury is still out on

why plants have leaf teeth.

 

Parrish said, " I think the authors have identified a very interesting

problem and have made progress toward trying to answer it. As to

whether this is the ultimate answer, that remains to be seen with

further studies, but the authors have kicked off a promising line of

research. "

 

Royer said the research is important because " we on Earth today are

experiencing rapid climate change. A problem with trying to understand

our current climate change is that it is an unreplicated experiment! "

 

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