Cleistogamous flowers are those small, inconspicuous blossoms of the late season that usually grow near the ground and never open. They are, however, fruitful, being self-fertilized within themselves. Violets bear them abundantly.
Leaves may be looked upon as appendages of the stem. They are the digestive organs of the plant and assimilate the sap into material for sustaining its tissues.
The Blade is the usually broad, flat part of the leaf.
Stipules are the two small blade-like parts at the base of the petiole. They are often inconspicuous, or absent.
Bracts are the modified leaves of an inflorescence or those that are under a flower. Usually they are green and of different size and shape than the rest of the foliage; sometimes, however, they are highly coloured and petal-like.
The three principal ways in which leaves are arranged upon the stem are:
Alternate: that is when one leaf appears just above the other on another side of the stem. (Fig. 27.)
Opposite: when two appear at each joint, having the semicircle of the stem between them. (Fig. 28.)
Whorled: when they grow at intervals in a circle around the stem. (Fig. 29.)
The Veining of the leaves is classed under two divisions: Netted-Veined and Parallel-Veined.
Netted-Veined leaves are those in which the veins branch off from the midrib and branch again into veinlets that run together and form a network, or mesh. (Fig. 30.) Netted-veined leaves are said to be Feather-Veined when the secondary veins all start from the sides of the midrib, running from the base to the apex of the leaf. (Fig. 31.) They are called Palmately-Veined when several veins of equal size start from the same point at the base of the leaf and spread out towards the margin.
Parallel-Veined leaves are those in which the main veins run side by side, without branching or running together. (Fig. 32.)
The veining of the leaves is always in complete harmony with their shape, so that much can be learned by noticing this feature carefully.
Leaves vary greatly in general outline, and the following terms are used to designate some of their common forms:
Linear: the narrowest form of a leaf - several times longer than broad: grass-like. (Fig. 32.)
Lanceolate: long and narrow, slightly broader at the base and tapering towards the apex. (Fig. 30.)
Oblanceolate is a reversed lanceolate.
Oblong: when two or three times broader than long. (Fig. 31.)
Elliptical: oblong but tapering at both ends. (Fig. 33.)
Oval: broadly elliptical. (Fig. 34.)
Ovate: when the outline is similar to the shape of an egg, the broader end downward.
Obovate: the reverse of ovate.
Spatulate: like a spatula, rounded at the apex and tapering towards the base. (Fig. 35.)
Orbicular, nearly circular or rounded in outline. (Fig. 41.)
Cordate or Heart-Shaped: when the outline is ovate, the sides forming a notch at the base. (Fig. 37.)
Obcordate: the reverse of cordate.
Reniform, or Kidney-Shaped: when the indentation is deeper and the leaf more rounded than heart-shaped. (Fig. 38.)
Auriculate: when the sides of the leaf are prolonged at the base into two ears or lobes. (Fig. 39.)
Sagittate, or Arrow-Shaped: when these lobes are acute and pointed backward. (Fig. 40.)
Peltate, or Shield-Shaped: when the leaf is orbicular, with the petiole attached to the middle. (Fig. 41.)
Entire Leaves are those in which the margins form an unbroken line. (Fig. 35.)
Undulate Leaves have margins that are wavy. (Fig. 33.)
Serrate Leaves have margins with short, sharp teeth that point forward. (Fig. 30.)
Crenate, or Scolloped: when the teeth are rounded. (Fig. 31.)
Incised: when the teeth are coarse and jagged and extend deeper into the leaf. (Fig. 34.)
Lobed: when the incisions extend about half way to the midrib; and in which case the leaf is spoken of as three lobed, five lobed, or according to the number of lobes formed. (Fig. 42.)
Cleft: when the incisions reach more than half way to the midrib. (Fig. 43.)
Divided: when the incisions extend to the midrib.
Compound Leaves have the blade split into separate parts, the little blades forming leaflets. When the leaflets are arranged similarly to feather-veins they are said to be Pinnate. When arranged as the veins in a palmately-veined leaf they are Palmate.
Abruptly Pinnate Leaves are those in which the main stalk is terminated by a pair of leaflets. (Fig. 45.)
Odd-Pinnate: when an odd leaflet terminates the stalk. (Fig. 46.) Sometimes this end leaflet is changed into a tendril, which aids the plant in climbing.
Leaves may be twice, thrice or more times compound. (Fig. 47.) The leaflets are subject to all the variations and may be described after the manner of simple leaves. In fact, the expressions here given are applicable to any flat part of the plant, the petals or sepals as well as the leaves.
Glaucous: when any part of the plant is covered with a powdery substance called a bloom.
Glabrous: when the parts are without bristles or hairs.
Pubescent: when covered with fine hairs or downy.
The Stem is that part of the plant that grows upward to the light and air, supports the foliage and makes it possible for the leaves to expand and present as large a surface as possible to the sunlight. Its manner of growth is described as being:
Erect: when growing up vertically.
Decumbent: lying on the ground but raising itself at the end. (Fig. 48.)
Procumbent: lying flat on the ground. (Fig. 49.)
Creeping: running along the ground and rooting at the joints. (Fig. 50.)
A Simple Stem is one that is not branched.
It is interesting to notice the wisdom with which stems accommodate themselves to the necessities of the plant. We find some stems growing entirely underground and storing up nourishment for the plant's growth during the next season. These stems are called the Rootstock and are distinguishable from the root by bearing scales, which are not found on roots proper. (Fig. 51.)
The Tuber is the end of a rootstock that is thickened or enlarged. The enlarged part is possessed of eyes (buds). The common potato is a familiar illustration of tubers. (Fig. 52.) The Corm is a rounded, compact rootstock. (Fig. 53.) The Bulb is a corm mostly made up of fleshy scales. (Fig. 54.)
The Scape is a leafless peduncle, or the flower-stalk of a plant that has no stem.
The Root proper grows downward in the ground and bears nothing but rootlets and root-branches. Its principal function in life is to absorb the nourishment from the soil.
Aerial Roots are produced in the open air and serve the plant by acting as holdfasts, or helping it to climb.
Parasites intermingle their roots with the roots or stems of other plants and drain from them their sustenance.
Thorns are modified branches. Their purpose is to guard the plant from animals that would strip it of its stem and bark.