MORPHOLOGY OF THE ANGIOSPERMS: TRILLIUM; DENTARIA.
=639. General appearance.=—As one of the plants to illustrate this group we may take the wake-robin, as it is sometimes called, or trillium. There are several species of this genus in the United States; the commonest one in the eastern part is the “white wake-robin” (Trillium grandiflorum). This occurs in or near the woods. A picture of the plant is shown in fig. 378. There is a thick, fleshy, underground stem, or rhizome as it is usually called. This rhizome is perennial, and is marked by ridges and scars. The roots are quite stout and possess coarse wrinkles. From the growing end of the rhizome each year the leafy, flowering stem arises. This is 20-30_cm_ (8-12 inches) in height. Near the upper end is a whorl of three ovate leaves, and from the center of this rosette rises the flower stalk, bearing the flower at its summit.
=640. Parts of the flower. Calyx.=—Now if we examine the flower we see that there are several leaf-like structures. These are arranged also in threes just as are the leaves. First there is a whorl of three, pointed, lanceolate, green, leaf-like members, which make up the _calyx_ in the higher plants, and the parts of the calyx are _sepals_, that is, each leaf-like member is a _sepal_. But while the sepals are part of the flower, so called, we easily recognize them as belonging to the _leaf series_.
=641. Corolla.=—Next above the calyx is a whorl of white or pinkish members, in Trillium grandiflorum, which are also leaf-like in form, and broader than the sepals, being usually somewhat broader at the free end. These make up what is the _corolla_ in the higher plants, and each member of the corolla is a _petal_. But while they are parts of the flower, and are not green, their form and position would suggest that they also belong to the leaf series.
[Illustration: Fig. 378. Trillium grandiflorum.]
=642. Andrœcium.=—Within and above the insertion of the corolla is found another tier, or whorl, of members which do not at first sight resemble leaves in form. They are known in the higher plants as _stamens_. As seen in fig. 379 each stamen possesses a stalk (= filament), and extending along on either side for the greater part of the length are four ridges, two on each side. This part of the stamen is the _anther_, and the ridges form the anther sacs, or lobes. Soon after the flower is opened, these anther sacs open also by a split in the wall along the edge of the ridge. At this time we see quantities of yellowish powder or dust escaping from the ruptured anther locules. If we place some of this under the microscope we see that it is made up of minute bodies which resemble spores; they are rounded in form, and the outer wall is spiny. They are in fact spores, the microspores of the trillium, and here, as in the gymnosperms, are better known as _pollen_.