THE DISCRETE ROOT EPIDERMIS OF FLOATING PLANTS

The reason why roots of some floating plants have a discrete epidermal meristem was investigated by comparing rates of anticlinal and periclinal division in shells of tissue during early development of lateral primordia of Pistia stratiotes L., which has such an epidermis, with those of Eichhornia crassipes (C. F. P. Martius) Solms‐Laub., which has not. The main factor involved is the timing and extent of the expansion of the primordium in relation to the availability of cells that can switch their divisions to anticlinal planes conformably with the growth of contiguous cells. The greater growth rate of the primordia of Pistia at the critical early stage forces the proximal cells of the endodermis‐derived tissue to divide only anticlinally immediately after their initiation by periclinal divisions and until the pole of the root forms a quiescent centre. It thus creates a monostromatic shell between the root cap and the pericycle‐derived tissue. Copyright © 1990, Wiley Blackwell. All rights reserved