In aeroplane design, the leading edge is either “the part of the wing that first contacts the air … or … the foremost edge of an airfoil section“. Plants – as one might expect – have a different take on that (and got there first).
Musing on the role played by trichomes [outgrowths from plant surfaces of diverse structure and function, e.g. hairs, scales, and papillae, George Wagner et al., Ann Bot 93: 3-11, (2004)] on leaf surfaces and margins (the edges of plants…), Gerjat Vermeij has come up with a rather interesting interpretation for the role that some of these structures might play in the interaction between plants and those animals that would cause them harm (Biological Journal of the Linnean Society 116: 288–294 (2015)).
Vermeij’s focus has been directed at so-called anisotropic (“anisotropy is the property of being directionally dependent”) trichomes – those arranged asymmetrically on the leaf surface – and which either point towards the tip of the leaf (apically-oriented), or towards its base (basally-oriented). Recognising that ‘small herbivores’ (e.g. insects) frequently move over the leaf surface – in search of a suitable part to chew on, or pierce with a stylet to abstract sugar-rich phloem sap, or a site to lay eggs – he proposes that the orientation of these trichomes may have a defensive role.
His suggestion is that the trichomes either facilitate insect locomotion towards the leaf tip (where they fall off) – in the case of apically-oriented hairs, or greatly hinders their movement towards the leaf tip (for basally-pointing trichomes). This is a hypothesis that needs further investigation – and other roles for these anisotropic features are not ruled out – but the thought of plants ‘leading insects on’ certainly raises a smile (and shows just how much we still don’t know about plants…).
Geerat J. Vermeij (2015) Plants that lead: do some surface features direct enemy traffic on leaves and stems?. Biological Journal of the Linnean Society 116(2): 288-294; http://dx.doi.org/10.1111/bij.12592