GROWTH AND DEVELOPMENT OF AERIAL ROOTS OF A TROPICAL ORNAMENTAL, PHILODENDRON LACERUM

Philodendron lacerum, an ornamental aroid, produces aerial roots and s ubterranean ones. The two root types differ in morphological, anatomic al and growth characteristics. Aerial roots, unlike the subterranean r oots, do not produce laterals. Anatomically, aerial roots are distingu ishable from subterranean roots by chlorenchyma and sclerenchyma cells in the cortex. Marked structural and growth differences exist between young and mature aerial roots. Mature aerial roots contain more scler enchyma cells and chloroplasts and larger resin ducts than young roots . The elongation rate of young hanging roots was much greater than tha t of mature ones. Aerial roots in contact with a substratum produce fe w sclerenchyma cells and chloroplasts on the contact side; their growt h rate, nonetheless, was not affected by the contact. Biochemical anal yses of the aerial roots revealed that the extractable protein content was highest at the growing root apex and chlorophyll concentration wa s highest in the mature portion of the aerial roots. The growing root tip portion exhibits a higher activity of alkaline phosphatase, acid p hosphatase and napthol AS-Bi-phosphohydrolase compared with the mature region of the aerial root. The activity of esterase, esterase lipase, leucine arylamidase, beta-galactosidase and N-acetyl-beta-glucosamini dase were detectable in the actively growing root tip region of the ae rial root but were very low or absent in the mature root tissues. Thes e findings are discussed in the light of the existing knowledge of aer ial root development and its role in ecological adaptation.