Fig. 164. Rootstock and equitant leaves of Iris. 165. A section across the cluster of leaves at the bottom, showing the equitation.
[160.] Equitant Leaves. While ordinary leaves spread horizontally, and present one face to the sky and the other to the earth, there are some that present their tip to the sky, and their faces right and left to the horizon. Among these are the equitant leaves of the Iris or Flower-de-Luce. Inspection shows that each leaf was formed as if folded together lengthwise, so that what would be the upper surface is within, and all grown together, except next the bottom, where each leaf covers the next younger one. It was from their straddling over each other, like a man on horseback (as is seen in the cross-section, Fig. [165]), that Linnæus, with his lively fancy, called these Equitant leaves.
[161.] Leaves with no distinction of Petiole and Blade. The leaves of Iris just mentioned show one form of this. The flat but narrow leaves of Jonquils, Daffodils, and the cylindrical leaf of Onions are other instances. Needle-shaped leaves, like those of the Pine, Larch, and Spruce, and the awl-shaped as well as the scale-shaped leaves of Junipers, Red Cedar, and Arbor-Vitæ (Fig. [166]), are examples.
Fig. 166. Branch of Arbor-Vitæ, with awl-shaped and scale-shaped leaves.
[162.] Phyllodia. Sometimes an expanded petiole takes the place of the blade; as in numerous New Holland Acacias, some of which are now common in greenhouses. Such counterfeit blades are called phyllodia,—meaning leaf-like bodies. They may be known from true blades by their standing edgewise, their margins being directed upwards and downwards; while in true blades the faces look upwards and downwards; excepting in equitant leaves, as already explained.
[163.] Falsely Vertical Leaves. These are apparent exceptions to the rule, the blade standing edgewise instead of flatwise to the stem; but this position comes by a twist of the stalk or the base of the blade. Such leaves present the two faces about equally to the light. The Compass-plant (Silphium laciniatum) is an example. So also the leaves of Boltonia, of Wild Lettuce, and of a vast number of Australian Myrtaceous shrubs and trees, which much resemble the phyllodia of the Acacias of the same country. They are familiar in Callistemon, the Bottle-brush Flower, and in Eucalyptus. But in the latter the leaves of the young tree have the normal structure and position.