Fig. 1

Adventitious roots that formed on tomato stems – morphology and three pathways of their emergence. a1-a3. Emergence by means of epidermis disruption observed in ‘young’ grafts or cut stems (I). a1. Multiple AR on a scion that had already emerged (open arrows) or were about to (arrow). a2. An empty space (open arrow) is formed between the AR (arrow) and the scion as a result of tissue loosening or lysis. a3. AR are covered with pectic substances at the root tip. b1-b3. Occurrence of an envelope enclosing AR observed on ‘older’ grafts only (II). b1. Envelope surrounds the developing AR primordia (arrows) but may be detached (inset), leaving intact roots (arrow). b2. Transverse section through an adventitious root (dotted line) enclosed within an envelope consisting of large parenchymatous cells (arrow); inset 1: the envelope originates from scion parenchyma cell division (arrow) and further cell proliferation; inset 2: root and envelope cells remain in close contact. b3. ARs formed on stems with secondary growth have a specific shape (dotted line) at the primordium stage and have a shape that is different from that of the ARs that formed on young stems. c1-c3. Occurrence of an oculus-like opening observed on cut stems only (III). c1. Oculus-like openings are visible before root emergence (arrows); their size is variable and they comprise of one or more emerging ARs (open arrows). c2. Openings filled with large, loosely attached callus cells (arrow) are established at an early stage of ARs development (primordium outline marked by dotted line). c3. Callus cells are of a parenchymatous origin (arrows). asterisk – callus cells, dag – days after grafting. Scale: 2.5 mm (a1, a2), 1 mm (b1, inset b1, c1), 0.5 mm (a2, a3, c1 inset, c2, c3)