PLATE I Figs. 1, 2, and 3. Cross sections of spines, showing the long epidermal cells underlain by several layers of cells which are slightly thicker-walled and whose contents stain much darker than the parenchyma tissue within. Figure 3 illustrates this difference most strikingly Fig. 4. Cross section of a reniform gland PLATE II Fig. 1. The epidermal and a few of the underlying cells, greatly enlarged, showing the dense protoplasm and the presence of the cuticle above. The typical condition before secretion Fig. 2. Similar cells after secretion. The cells are vacuolated, the cuticle has been pushed away from the epidermis, and the remnants of the secretion can be seen |