Fig. 4.1-3. Transverse section of petiole of water lily (Nymphaea). This is the region where fully-formed collenchyma (at the top of the micrograph) grades into ordinary parenchyma (at the bottom). Near the top, it is possible to see the middle lamella between several of the cells, and because the middle lamella is straight, so is the outer surface of the cell wall – these cells really are angular, not spherical. Notice that there are intercellular spaces between the parenchyma cells and collenchyma cells and even between some of the innermost collenchyma cells.