Origin and nature of vessels in monocotyledons. 4. Araceae subfamily Philodendroideae

Tracheary elements of roots and rhizomes of five species of Araceae, subfam ily Philodendroideae, representing five of the seven tribes of the subfamil y, were studied by means of SEM, using macerations supplemented by sections . All except Zantedeschia albo-maculata and possibly Anthurium scherzerianu m proved to have vessels in rhizomes as well as roots; only vessels in root s have been previously reported for the family. Perforation plates of rhizo mes differ little from those of roots, although in some of the species pit membrane remnants are more conspicuous in rhizome perforation plates. The w ell-defined perforation plates of Anthurium may be related to conduction wh en water is available in terrestrial and epiphytic habitats that dry season ally. Likewise, the root vessels of Zantedeschia may be related to rapid co nduction during wet periods. Vessel elements of subfamily Philodendroideae represent features regarded as primitive, most notably, similarity between perforations and lateral wall pits, and the presence of pit membrane remnan ts in perforations. Pit membrane remnants likely are little impediment to c onduction in moist tropical understory localities where most aroids grow.