secundum dealt with plants cultivated in greenhouse conditions, and described roots with five-six layered velamen, exodermal cells with wall thickenings, 10-12 layered cortex, O-thickened endodermis, and 17 protoxylem poles.
The passage cells are small, quadrangular in TS, with dense cytoplasm and interpolated by the other exodermal cells (Fig.
There are some pentagonal and alive passage cells with dense cytoplasm, usually smaller than the other exodermal cells.
Similarly to the velamen, the exodermal thickenings aid in reduction of water loss by root transpiration (Benzing et al.
The thickening of the external cortex cell walls can be homogeneous as in Pycreus macrostachyos (Figure 10--amphibious species), or more intensive in the first cell layer of the external cortex as in Cyperus odoratus (Figure 13--amphibious species), or the internal wall of the exodermal
cells can be thinner than the outer periclinal one, as in Eichornnia paniculata and Echinodorus grandiflorus (Figures 11-12,14--emergent species).