Fig. 3. Laser ablation of the site of incipient leaf formation (I₁) affects phyllotaxis. (A-H) Two individual tomato apices imaged from the top, 1 day (A,E), 2 days (B,F), 3 days (C,G) and 4 days (D,H) after laser ablation of I₁. (A-C,E-G) light stereomicrographs; (D,H) SEM images. (A) The site of incipient leaf formation (black arrowhead) was ablated with 10 successive laser pulses as described previously (Reinhardt et al., 2003b). (B) I₁^* initiates adjacent to the ablation. The divergence angle between P₁ and I₁^* is increased to approximately 175°, whereas the angle between I₁^* and I₂ (C) is smaller than normal (107°). The following angle between I₂ and I₃ (D) is normal again (138°). (E) Ablation as in A. I₁^* was formed just above P₂ (F), resulting in the reversal of the phyllotactic spiral from an anti-clockwise to a clockwise direction (G,H). P₄, P₃ and P₂, indicate the bases of pre-existing leaf primordia that were removed at the beginning of the experiment, and P₁ represents the youngest primordium; I₁, I₂ and I₃ indicate primordia formed after the ablation. Scale bar: 100 µm.