| MadSci Network: Botany |
Hello Vishal,
This is a very difficult kind of question to answer. It requires speculation on the selective advantage of different arrangements of vascular bundles, which is very hard, if not impossible, to test experimentally. Plants exhibiting the various vascular bundle arrangements can be found living side by side in the same environment, so it’s hard to make a compelling argument that different bundle types are suited to different environments. A similar type of question would be to ask why oaks and maples and elms each have different shaped leaves. It’s hard to imagine slightly different leaf shapes provide much, if any advantage. It could just be a quirk in the evolution of those lineages. Not every variation seen between species is necessarily an adaptaion. In other words, not every feature of an organism provides a selective advantage.
The only clear advantage I can think of can be seen in trees. The arrangement of vascular bundles in trees, both angiosperm and gymnosperm, allows for extensive secondary growth (ie increases in diameter) of stems, which is how wood forms. The apparent advantage of wood is its strength, which allows trees to grow to great heights. In this case, the ability to grow tall in search of more light could very well provide a strong selective advantage in a crowded environment. In addition, the durability provided by wood may contribute to the longevity of trees, some of which live for thousands of years. Palms also form a kind of woody trunk, but secondary growth is limited because of the arrangement of the vascular buncdles, which limits the height.
Other vascular bundle arrangements don't have such obvious advantages, at least none that I can find any information or speculation on.
Dr. Alex Brands
Lehigh University
Try the links in the MadSci Library for more information on Botany.