Stamen structure

Pollination an important step in the reproduction of seed plants—the transfer of pollen grains (male gametes) from the stamens (male organs) to the plant carpel, the structure that contains the ovule (female gamete). The receptive part of the carpel is called a stigma in the flowers of angiosperms (flowering plants). 

Species of the mulberry family may be either monoecious or dioecious, depending on whether male and female flowers occur on the same plant (monoecious) or on separate plants (dioecious). Flowers of the Moraceae are in tightly packed groups, known as heads, spikes, catkins, or umbels. Fig flowers are produced inside a synconium, a hollow fleshy structure. The small flowers lack petals. Male flowers consist of four sepals, which are usually leaf-like appendages, and four stamens. Female flowers consist of four sepals and a pistil with a two-chambered ovary. 

The flowers of members of the Brassicaceae have four petals arranged in a cross-like pattern (the old name for this family was Cruciferae, referring to the cross of crucifixion). The flowers of mustards contain both female and male parts (i.e., they are monoecious). There are six stamens, of which four have long filaments, and two have short filaments. The seeds of plants in this family are contained in a relatively long inflated structure called a silique, or in a rounder flattened structure known as a silicle. When mature, the outer walls of the fruits fall away, leaving an inner partition to which the seeds are loosely attached. 

Color of Stamens.—In most spedes the color of these organs is seldom pronounced owing to their delicate structure. It varies from greenish-yellow to yellow to white, through pink, pinkish-red, red, purple, purple-blue to blue. It is yellow, for instance, in Sassafras, Cucumber and Golden Club greenish-yellow, yellow to red, in Maples yellow-pink to pink and pinkish-red, in some Mallows in Azalea amena the filaments are crimson-purple and the anthers, purple-blue in the genus Scilla both filaments and anthers are blue. 

PlG. 167.—Diagram of A, lily flower, and B, grass flower, showing homologous structures. A, f, bract ax, axis op, outer perianth ip, inner perianth r, stamens (c) tricarpellary ovary. B, shaded structures are aborted le, lemma (bract) ax, axis p and p, palet (outer perianth) I and V, lodicules (inner perianth) r and s, two whorls of stamens c, tricarpellary ovary. (A, Robbins. B, after Shuster.)... 

Fil ament.—The stalk of a stamen a thread like structure. 

Coronai a corolla-like structure within the whorl of the corolla, usually derived from the stamens (see the tube in Narcissus., or the often hornlike structures in many Aacle-piadaceae). 

The need for a system with useful principles of classification has long existed, and the progress of research has changed the character of these systems. Thus, the system, introduced by Linne (Linnaeus), was a purely artificial system for phanerogams, built on the structure of the flower and the number and arrangements of stamens and pistils. 

In the more benign asexual cycle, Epichloe endophytes (and all Neotyphodium species) remain asymptomatic (Fig. 1). As floral primordia are formed, endophytes grow into ovules, proliferate in the nucellus tissues, and later colonize the embryonic axis of the developing seed, which leads to vertical transmission (Freeman, 1904 Philipson and Christey, 1986). Hyphae in the remnant nucellar layer form a conspicuous mat between the aleuron and the seed coat (White et al., 1991). Symptomless endophytes may also invade stamen filaments and anther walls, but have never been found in pollen grains, and apparently are not disseminated via paternal structures (Sampson, 1933 Hinton and Bacon, 1985). Vertical transmission of endophytes in infected tillers occurs at nearly 100% efficiency (Siegel et al., 1984). However, seeds which are free of endophyte may occasionally be produced when shoot meristems of individual... 

Multimode breakup occurs at values of We between those of bag- and sheetthinning and resembles a combination of the two breakup modes. Bag formation accompanied by the presence of a core drop results in the formation of a long ligament in the center of the bag, which is referred to as a stamen or plume [1,16], The third image in the second row of Fig. 6.1 illustrates the bag/plume structure. 

Androecium - The androecium consists of at least six structures that are interpreted as nectariferous, and three stamens or staminodes of which only the fila-ments/filament bases are preserved. The nectariferous structures are arranged in pairs and each pair is associated with a more centrally placed filament/filament... 

The presence of a basally united perianth composed of two distinct perianth whorls, and an androecium with at least one whorl of stamens associated with stalked, presumably nectariferous, structures in Powhatania connata indicates a relationship to extant Laiuales. The stalked structures are distinctive in their shape and position. They are free with semi-peltate/peltate heads and occur in a lateral position to the stamens of the first androecial whorl. 

Together Cohongarootonia, Potomacanthus and Powhatania demonstrate that a basically trimerous floral structure, including stamens with or without paired... 

The subclass Dilleniidae was introduced into angiosperm macrosystematics by Takhtajan (1964) largely influenced by the occiurence of centrifugal stamen initiation in polymerous androecia, which was supposed to be a fundamentally important pattern in macrosystematics. However, the subclass was later dismantled, first by structural cladistic studies (Hufford, 1992) and then also by molecular studies (Chase et al., 1993) (see also Endress et al., 2000). From the present perspective, the feature is not stable at very high systematic levels, however, often it is still at family level. 

---