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| Cook pines lean to wherever the equator is |
The growing of tree is influenced by two things which are in respond of light and gravity, but the most influence is made by the demands of light. The soybean for instance, this plant will grow to where the light is produced. On the other hand, the trees may grow in non-vertical directions if there is competition of accessing light created by the others trees. But, the Cook pines or Araucaria columnaris grow to the hemisphere whether they were grown in the southern or northern part of the Earth.
This phenomenon was firstly realized by biologist named Jason W. Johns of California Polytechnic State University [1]. The scientists conducted and measured the 256 trees which were grown in five continents in 18 different regions. To obtain precise data, the measurements were conducted for trees that have been placed more than 500 km from each other. According to the scientist, every tree was measured in four characteristics so the position of leaning can be calculated throughout recording the height, trunk diameter above one and half meter from the ground, azimuth direction and the extent of the lean.
The results were amazing. With 7 to 35-degree North and 12 to 42-degree South latitude, the Cook pines grow in constant and consistent pattern. The leaning is always to the equator or by quoting the statement, “a surprising consistent pattern of hemisphere-dependent directional leaning on Araucaria columnaris”. If they grow in the northern hemisphere, the Cook pines lean south with median azimuth of 115-degree. While the Cook pines located in the southern hemisphere, then they lean to the north with median azimuth of 0-degree. This result was astonishing because instead of merely influencing by the light and gravity, the growth of Cook pines is influenced by the magnitude and latitude of the Earth.
Based on the discussion written on their paper, the reason of the leaning is remained unclear since the until now the natural growth of trees only have been depending on negative gravitropism and positive phototropism which were respectively coined by Hashiguci and Darwin. Whereas the another non-vertical growth was occurred by the presence of mechanical perturbation suggested by Tomlinson in 1983 and Telewski 2006.
Although the scientific reason lies on the leaning process of growth on Cook pines is still secret, the hypothesis from this report could lead into the relationship of plants responses to environment.
References
[1] J. W. Johns, J. M. Yost, D. Nicolle, B. Igic and M. K. Ritter, "Worldwide hemisphere-dependent lean in Cook pines," The Scientific Naturalist, vol. 0, no. 0, pp. 1-3, 2017.
[2] Image is downloaded from New Scientist