ANATOMICAL FEATURES OF METAPHLOEM IN STEMS OF SABAL,COCOS AND TWO OTHER PALMS

Sieve tubes in metaphloem of palm stems function throughout the life of the plant and merit close investigation. A stem of Sabal palmetto estimated to be 50 years old was sampled extensively. Variation in length of sieve-tube elements throughout this stem was measured and is discussed. In the metaphloem of individual vascular bundles companion cells are not sharply differentiated from other phloem parenchyma cells. Definitive callose deposits and slime are normally absent from mature sieve tubes, even in fixed material. Otherwise no conspicuous structural features which might account for the longevity of sieve tubes can be discerned. Occlusion of phloem strands after leaf fall is initially by callose deposition on sieve plates followed immediately by tylosoid formation. Similar sampling of Cocos nucifera, Washingtonia robusta and to a lesser extent Archontophoenix alexandrae confirmed these results except for quantitative differences.