Fig. 2

Histology of adventitious roots from tomato-grafted stems. a Division of the initial cells (arrow) and thickened walls at the AR/scion tissue border (open arrow); asterisk – multicellular complexes. b Meristematic cells of a young primordium (arrows) and scion cells (open arrow). c AR bearing LR initials (open arrow) and cell divisions in the parenchyma (arrows) next to a developing AR (asterisk); inset 1: LR pericycle origin (open arrow); inset 2: thick layer between the AR and scion (arrow). d Callose in the phloem (ellipse) and the layer between the AR (dotted line) and scion (arrow); inset 1: callose in the primary pit fields (open arrows) and cell plate (arrow); inset 2: callose (arrows) between the AR/LR border. e Polyphenols in the rhizodermis (arrows) and periclinal cell divisions beneath (open arrows); inset: older AR, lipids in the phellem (arrow). f Transverse section, AR (dotted line) enclosed within the envelope covered by lipid substances (open arrow), no lipids in the rhizodermis (arrow); inset: envelope cuticle (open arrow). g, h AR emerging by means of epidermis disruption; the root cap file starts at the edge of the primordium (circled area) and comprises 1 to 2 cell files (arrows), adjacent to layer of dead cells (open arrow). i AR primordium (dotted line) emerging within an envelope; root cap cells (arrow) adjacent to a layer of dead cells (open arrow). j Root cap cells of various sizes (arrows) next to dead cells (open arrow). k Root cap cells (arrows) after emergence. ar – adventitious root, c – cambium, col – collenchyma, cor – cortex, e – endodermis, lr – lateral root, p – pericycle, rc – root cap. Scale: 100 μm (c, d, e, g, i, k), 50 μm (a, b, f, h), 25 μm (f inset); 10 μm (c inset 1 and 2, d inset 1 and 2, e inset and j)