Learn to Draw and Paint Trees, Landscape Art Instruction
CHAPTER XIX SHAPES OF FLOWERS
THERE is as great a variety in the forms of the florets themselves as there is in their inflorescence. This will be best understood if we describe a typical flower ; then the discrepancies in others will be appreciated.
A flower is made up of separate parts, that have a distinct mission to fulfil in their business of reproduction. These are (1) the essential organs of reproduction--the Stamens (male organs) and the Pistil (female organ). (2) The leafy envelopes that protect them.
A flower which is composed of (1) and (2) is called a " Complete " flower ; all its parts are arranged on a more or less convex form, which is the enlarged extremity of the flower-stalk, and is called the Receptacle (Figs. 261-265). Each set of organs is arranged in a circle on the receptacle, one circle surrounding another. Taking these sets in order from the base (nearest the stalk on the out side of the receptacle), we find (a) an outer envelope called the Calyx. This usually consists of separate leaves, green in colour, called Sepals ; sometimes they are united so as to form a collar. (b) Inside the calyx is the next envelope, called the Corolla. This is usually brightly coloured ; commonly consisting of separate forms called Petals, but occasionally composed of an entire circular funnel. (c) The third circle is composed of stamens ; each of these is constructed of a stalk named the Filament and a head called the Anther (the latter being of twin cells containing the fertilising material called Pollen). The central form round which all the others radiate is this Pistil --the female organ of reproduction. The base of this pistil is called the Ovary. It contains the ovules (which, after fertilisation by the pollen,become the seeds). On the apex of the ovary is the Stigma. This receives the pollen, and it is usually connected with the ovary by a cylindrical stalk called the Style. This diagram (Fig. 264) of a vertical section of a flower explains the order of these parts on the receptacle. The plan of the flower (seen from above), Fig. 265, shows how the parts are arranged in circles, and the alternating arrangement of the individual forms.
Illus. 125. Example of "Complete" Flowers - The Cherry
The Calyx and Corolla are usually each made up of five parts-5 sepals, 5 petals--examples, Apple, Lime, Plum, Maple, etc. (Fig. 266) ; commonly the stamens are numerous, but their number is some multiple of five--such as thirty. Flowers made up of four parts (Fig. 267) are not uncommon-4 sepals --4 stamens --4 petals (examples, Cornel (Illus. 127), Spindle). The parts of each circle, whether they are five or four in number, alternate with the parts of the next circle; so that in a four-petalled flower the forms of each circle would by themselves form a cross, and each cross would alternate with the next (Fig. 268). In this way the sepals and stamens would lie in the same direction--forming two Saint Andrew's crosses, while the petals would make a Greek cross between them. To save confusion of terms, we called the female organ simply a pistil ; but to make the change from flower to fruit understood, we must explain its construction further.
A Pistil may be theoretically considered as made up of one or more modified leaves. These modified leaves are called carpels, and are either separate, united, or partly united together, to form the pistil. That they are merely transformed leaves will be seen by examining the central forms of a double Cherry flower, where they retain the leaf forms, and comparing them with the pistil of a single cherry flower, where the same forms will be found, but united at the margins, to form a single carpel. Carpellary leaves can also be found in a simple pistil, in the " neuter " flowers of the Holly and Guelder-Rose (Figs. 270 and 278), and other trees, instead of a pistil. In a simple pistil the margins of a carpellary leaf are turned inward to form the wall of the ovary, and are turned outward at the tips to form a two-lipped stigma. A Compound Pistil may be formed either of single carpels adhering to one another so that the ovary is divided into the cells (one cell created by each carpel), or several carpels may be united--the margin of one to the margin of another--and thus make an undivided ovary. Examples of compound pistils are provided by the female flowers of Oak, Beech, Hornbeam,
ILLUS. 126. EXAMPLE OF " COMPLETE " FLOWERS--THE PEAR
ILLUS. 127. EXAMPLE OF A FOUR-PETALLED FLOWER-THE CORNEL
Fig. 274 - Hawthorn
THE SHAPE OF FLOWERS ON SOME TREES
and Hazel--in these the ovary is divided into separate cells ; examples of Simple Pistils, by the flowers of the Plum and Cherry.
A complete flower, such as we have described, contains within itself the necessary fertilising medium (pollen), also the ovules capable of being fertilised.
Fecundation may be effected by the pollen being dropped direct on to the viscid surface of the stigma, that retains it ; but it is a curious fact that this is not of common occurrence. It is more interesting that the prevention of self-fertilisation is brought about by the habits of the flowers. Some flowers mature the stigma before the pollen is ripe (example, Birch), others allow the pollen to ripen and be dispersed before the stigma is ready to receive it. In these cases, cross-fertilisation between different trees has to be effected ; and we recognise the use of the gay colouring of the petals and the sweet scents of flowers in attracting insects that may act as transferring agents from one tree to another. The pollen of those flowers which are not endowed with bright- coloured petals is usually carried by the wind, as happens with the Scots Pine, Spanish Chestnut, Yew, and Oak. Lubbock has pointed out that flowers are the most susceptible to fertilisation from the pollen of the flower of another tree. Cross-fertilisation, it seems, is beneficial ; and is the rule rather than the exception. The bearing on the forms of flowers leads to great diversity of construction. (Figs. 269-289, pp. 266-8.)
The flowers on some species of tree are " complete," as we have described. In other species the flowers on individual trees contain either the male organs or the female organs, but not both, though they may carry calyx and corolla. In other cases the flowers on all the individual trees of a species consist of nothing but the simple functionary organs.
Again, in some species, individual trees bear both " complete" and unisexual flowers--sometimes separately on distinct branches, at other times grouped together in the same flower-cluster. Instances even have been noticed in which a branch would bear one type of flower one year, and another type in the following year, but this it; exceptional.
In some flowers the calyx and corolla are missing (example, Ash, Fig. 290) ; in some units of a flower-cluster it is the stamens and pistil that are missing, as in the outer circle of the Guelder-Rose (when the flower is called neuter). On many trees the flowers have neither calyx nor corolla, but consist of a scale and stamens (Figs. 291, 293), or a scale and pistil (Figs. 292, 294). This is the rule in the
ILLUS. 128. FLOWERS OF THE GUELDER-ROSE " NEUTER " FLOWER IN CIRCLE ENCLOSING " COMPLETE FLOWERS "-EXAMPLE OF TWO TYPES CONTAINED IN ONE CLUSTER
Willows and Poplars ; and a still more elementary form is shown in the Pines and Firs--either of a scale bearing a pair of anther lobes, or a scale carrying two naked ovules without any style or stigma.
The terms given to these different forms are (1) Complete --when the calyx, corolla, stamens, and pistils are present ; (2) Incomplete--when either calyx or corolla, or both, are missing, but stamens and pistil are present ; (3) Male--when the stamens are present, but not the pistil ; (4) Female-- when the pistil is present but not the stamens ; (5) Bisexual --when both the stamens and pistil are present.
When the individual tree bears both " Male " and " Female " blossoms, it is said to be Monceeious (examples, Birch, Hazel, Alder, Oak). The male organs must be in one flower, the female organs in another, but not both combined in the same flower.
If the individual tree bears either " Male " or " Female " blossoms, but not both, it is Dicecious (examples, Buckthorn, Poplars, Willows).
(When Bisexual, Male, and Female blossoms are on distinct trees ; the term used is Tricecious, as in the Spindle tree.)
(4) More rarely the tree bears Bisexual flowers as well as unisexual flowers, so that some florets have the organs of both sexes and other florets the organ of one sex only ; this is described as Polygamous. Sometimes the bisexual florets will be on one tree, and the unisexual florets on another tree of the same species. The Ash is a good example ; one individual tree may bear only male flowers, another individual tree may carry only female flowers, while a third may carry both bisexual and unisexual flowers. It is said that the same branch on an Ash tree may produce different types of flowers in different years. Holly trees are usually dicecious, but sometimes polygamous. The individual florets of many flowers are themselves inconspicuous, though the flower-cluster may make a brave show.
The appearance of some tree flowers bears so little resemblance to our notion of a flower that it is difficult to recognise them as such. The complete flowers of the delicate Apple blossom ; the swagger pyramids of florets on the Horse Chestnut ; even the little star-shaped flowers of the Spindle with petals of humble green, we immediately recognise as flowers. Other examples are Hawthorn, Cornel, Wayfaring tree, Elder, Whitebeam, Cherry, Bird Cherry, Mountain Ash, Pear, Lime.
Some of the incomplete flowers also remind us of the flowers of our garden, since they have petals, though other parts are missing ; for instance, the Buckthorn and Holly, where the male and female organs are on separate flowers. In others we see little resemblance ; such as in the catkins of the Birch, Willow, Oak, Sweet Chestnut, the Alder,
ILLUS. 129. CATKINS OF THE HORNBEAM
ILLUS. 130, THE HAIRY CATKINS OF THE ASPEN
ILLUS. 131. MALE AND FEMALE FLOWERS OF THE ALDER-EXAMPLE OP A " MONCECIOUS " TREE
ILLUS. 132. EXAMPLE OF MALE CATKINS ON A " DICECIOUS " TREE
ILLUS. 133. FEMALE FLOWERS OF WALNUT-EXAMPLE OF A " MONOECIOUS " TREE
ILLUS. 134. MALE CATKINS OF WALNUT
Hazel, and Hornbeam, or in the tassels of the Beech and budlike clusters of the Ash. Many of these flowers, however, from their colour, or profusion, affect the appearance of the tree as a whole. The Alder and Hazel " lambstails," and the clothing of purple-red flowers on the Elms, that come to the call of Spring, the sulphur catkins that cover the Birch ; and the gilded halls of the Goat Willow, sweet in scent and musical with the sound of countless bees before winter has waned, are each in their turn landmarks of the country. The crimson catkins of the Black Poplar give colour to the trees and the earth below, and the tiny ruby gems of the female Hazel flower, and the rose and white stigmas on the Walnut, are worth the seeking. The Scots Pine, prolific with its pollen, dusts all around with its sulphur-coloured clouds.
Individual trees of the following species bear either male or female flowers (not both)--the Willow, Poplar, and Aspen.
Individual trees of the following bear separate flowers of both sexes--Beech, Oak, Alder, Hazel, Hornbeam, Birch, Walnut, Holm Oak, Sweet Chestnut (male and female flowers on the same catkin), Spruce, Plane, Yew (sometimes), Box, Spindle (occasionally). The flowers of the Box are in clusters in the axils of the leaves. The male flowers are below the female on the same cluster. The Guelder-Rose has a flower-cluster composed of a number of complete flowers encircled by a row of neuter flowers (illustration, p. 270) (i.e. no pistil nor stamens). The Holly bears complete male and female flowers on the same tree, or bears only male or female flowers. Neuter flowers are also to be found.
We will now consider the shapes of flowers. The flower is " regular,"when all the parts of the calyx or corolla respectively are shaped alike ; of this the Apple or Blackthorn flower is a good example. It is " irregular " when the parts of either of these circles are dissimilar (examples, Horse Chestnut, Laburnum, Acacia).
The construction of flowers is various ; but three forms may be taken as types : (1) Normal construction, in which the receptacle is a dome supporting the central pistil while the calyx, corolla, and stamens are arranged in circles,
each circle in the above order from the base (Fig. 295). (2) The receptacle no longer a dome, but cup-shaped, with the pistil arising from the bottom of the cup, and the calyx, corolla and stamens carried on the rim of the cup (Fig. 296).
(3) The receptacle planned as in No. 2 ; but enclosing the ovary, leaving only the stigmas, or the stigmas and style, projecting from its adherent walls (Fig. 297). In the first and second plans the ovary is quite free, and consists of the carpels only. In the third plan the wall of the ovary is formed by the receptacle. It may be sufficient if we describe the ovary in (1) and (2) as " free," to distinguish it from (3), where it is " adnate." The purpose of such a definition will be seen in the following chapter in reference to the construction of fruits. In most flowers the sepals, petals, and stamens fall off after the fertilisation, leaving only the pistil ; or the ovary alone may be left. Often the calyx remains, and in some cases the bracts also. All the cells, or the ovules they contain, do not always come to maturity. Some persistently fail (example, Oak, Hazel, Birch).
Flowers not only give a new colour to trees, but for the time being alter their appearance in other ways. We see the twigs of the Elm, that through the winter have formed delicate tracery against the sky, become in March suddenly thickened and by comparison clumsy ; though the loss of pattern is atoned for at a distance by the changing colour. Birches, too, whose twigs were but a haze of lovely tone against the light, have their sky spaces filled in by a multitude of catkins far denser than the opening leaves.
All these matters are common knowledge to the country man ; but less obvious, though of greater importance, is the fact that the growth of the tree is stopped at those points where flowers are produced, and the new shoots starting from other points give the branches a new direction. But this is explained in the chapter dealing with Twigs.