As one of the most obvious indications of growth, you might have thought that there was little new to discover about increase in length of plant stems. Wrong! Studying growth in Iriartea deltoidea (Arecaceae), Heidi Rinninger and Nathan Phillips have uncovered an ‘efficient and novel method for height growth’. Typically, one is taught that increase in height of trees – primary growth – is the result of apical meristem activity (formation of new cells near the end of the stem that increase in length as they develop and differentiate comparatively close to the meristem). But in this palm the duo found that stems were lengthening after their tissues were differentiated and far below the apical meristem. Although such a phenomenon might be presumed to damage the non-extensible, mature conducting cells of the vascular tissues, the vascular bundles are laid down in a spiral which apparently ‘unwinds’, resulting in the observed length increase. The pair consider this so-called ‘secondary lengthening’ not only to be the most efficient method for height growth in terms of carbon investment, but also a mechanism that permits plasticity in height growth rates for more rapid growth when short-lived canopy gaps are present than they would have with apical growth alone. As they tantalisingly conclude, ‘This finding also highlights the fact that in addition to biodiversity, tropical rainforests also contain a high degree of “physiological” diversity, the depth of which is just beginning to be discovered’. Slinky!
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