A) Mechanical support at young stem and leaf petiole — III: Collenchyma tissue provides flexibility and support in growing stems and petioles.
B) Cells in fruit walls of nuts — I: These are made of sclereids, a type of sclerenchyma, giving hardness to nuts.
C) Cells absent in primary phloem — IV: Bast fibers (sclerenchyma) appear in secondary phloem, not primary.
D) Endarch primary xylem — II: Found in stem vascular bundles where protoxylem is towards the center.
Thus, correct match: A-III, B-I, C-IV, D-II.