Figure 1.

Pinecone seed scale functional morphology and kinematics. The scales passively react to changing environmental humidity conditions leading to a closed cone when it is wet (a) and to an open cone when it is dry (b). A longitudinally halved cone in the dry condition (c). The actuating sclereid layer is not tightly connected to the sclerenchymatous strands, which are embedded in a matrix of ‘brown tissue’ (sensu [15]) (d,e) and reach towards the apical apophysis (f). Images (d–f) modified from [16]. Light microscopy image of a semi-thin cross section of the functional bilayer set-up (g), one sclerenchymatous strand (h), a detail of the sclereid layer (i), a detail of the sclerenchymatous strand (j), and a detail of the ‘brown tissue’ (k). Fluorescence microscopy of an acridine orange-stained semi-thin longitudinal section of a scale (l). The brightness indicates degree of lignification, which is of increasing intensity in the sclereid layer towards the sclerenchymatous layer, high in the sclerenchymatous strand itself, and low in the ‘brown tissue’ (abbreviated as ‘B.’). (m) The bi-axial, two-phase, passive-nastic movement of the Bhutan pine (Pinus wallichiana) seed cone scale. An initially wet seed scale (in frontal and lateral view, clamped with its basal part by a forceps) undergoes two successive bending deformation processes upon desiccation (at approx. 20°C, approx. 50% RH). At the beginning (t = 0) the scale is wet, straight (without any conspicuous longitudinal curvature) and possesses a notable transversal curvature by which longitudinal bending is hindered. After t = 15 min, the transversal curvature alone has markedly decreased. Afterwards, the scale starts to bend longitudinally until a maximum bending angle (which depends on the extent of scale desiccation, i.e. on the environmental conditions) is achieved after t = 60 min. (Online version in colour.)