Fig. 4.1-2. Transverse section of stem of ivy (Hedera helix). This micrograph shows three layers of collenchyma cells in an early stage of development, before the corners have become very thick. It is possible to see that the cells actually are angular, not round, and with no intercellular spaces between the collenchyma cells themselves. As development continues, the corners would thicken even more and cell lumens would become round as in Fig. 4.1-1. The uppermost layer is the epidermis, and the lower, larger cells are ordinary cortex cells. Notice that there are intercellular spaces between the innermost collenchyma cells and their neighboring ordinary cortex parenchyma cells. Also, the innermost collenchyma cells have thickened corners where they abut other collenchyma cells but not where they abut parenchyma cells.