Fig. 2.

Pollen-tube growth and development of ovule and embryo sac in older pistils of Alnus.(A) Female inflorescence ≈7 weeks after pollination. (B) A single pistil detached from A.(C) Longitudinal section (LS) of ovary. (D) Magnified view the top box in C, showing the disappearing starchy grains in the cells of the style. (E) Magnified view of the bottom box in C, showing a tetrad of megaspores in the nucellus. Arrowheads indicate three degenerating megaspores. (F) Magnified view of the middle box in C, showing that the pollen tube lies in a zigzag line and is divided into small branches (arrows) on the surface of the upper region of the ovarian locule. (G) A diagram illustrating pollen-tube growth in an older pistil. Bold curved lines show pollen tubes and the gray shading shows cells which contained many starch grains in the younger pistil. es, one-nucleate embryo sac; ova, ovary; ovu, ovule; vs., vascular tissue; wg, wing. (Scale bar, 10 mm in A, 1 mm in B, 500 μmin C, 100 μmin D and F, and 50 μmin E.)