Grapevine inflorescences are initiated in an embryonic state as early as within the wintering buds. Shortly after budburst, the inflorescences become clearly visible: at this stage, they consist of a short central axis bearing clusters of as-yet undifferentiated flower buds, which present the appearance of dense cones enveloped by membranous, early-abscising bracts (Fig. 28).
A fully developed, typical grapevine inflorescence is a panicle (compound raceme) of a conical shape. Branchings of the 2nd order diverge in all directions from the central axis of the inflorescence, bearing in turn branchings of the 3rd order, upon which very short, stump-like axes of the 4th order are occasionally formed. Branchings of all orders are equipped at their base with small, early-abscising scale-like leaflets; however, individual flower buds are devoid of bracts.
The branchings of the 2nd order develop unevenly: they achieve their maximum length in the lower portion of the inflorescence, and as they approach the apex of the inflorescence, they become significantly shorter, as a consequence of which the entire inflorescence as a whole assumes a pyramidal form. A similar sequence is observed in the development of the axes of the 3rd order. However, inflorescences vary greatly among different grapevine cultivars in both shape and size.
In certain cultivars, the inflorescences become diffusely ramified due to a highly vigorous development of the 2nd-order axes (for instance, in cultivars Nimrang, Yakdona, etc.); in other cases, owing to a relatively weak and uniform development of all 2nd-order axes, the inflorescences acquire the shape of a rather regular cylinder (for example, in cultivars Pinot franc, Trebbiano, etc.).
The lowermost part of the primary axis of the inflorescence, which diverges directly from the shoot, is termed the "peduncle", while the entire system of inflorescence branchings as a whole is called the "rachis". In most grapevine cultivars, a thickened area (node) can be observed on the peduncle of the inflorescence, from which a tendril diverges, also bearing a scale-like leaflet at its base; sometimes this tendril dries up and abscises shortly after flowering, but not infrequently it persists and bears several flowers at its tip, or even transforms into an entire small inflorescence itself (a "wing").
Detailed investigations by Prof. A. S. Merzhanian in the field of grapevine inflorescence morphology demonstrated that the branching system of the inflorescence possesses a monopodial character. The tendril on its peduncle is always directed downward, and the first (i.e., the lowermost) pair of branchings following it lies in a plane perpendicular to the plane of the tendril; the second pair of branches is situated perpendicular to the first, the third pair perpendicular to the second, and so on. This pattern manifests with sufficient clarity only in the lower portion of the inflorescence and is gradually obscured as it approaches the apex.
Furthermore, when considering the inflorescence in connection with its bearing shoot, more flower buds are formed on the side of the inflorescence that corresponds to the "dorsal" side of the shoot; they bloom earlier and yield a greater number of set berries. Subsequently, the berries developed on the "dorsal" side of the inflorescence begin to ripen earlier and possess larger sizes than those on the "ventral" side.
On the branchings of the ultimate order (typically the 3rd, rarely the 4th), flowers are situated, arranged spirally around their bearing axis. Flowers may be positioned singly or in groups of 2–3 and more: the longer the inflorescence branching, the more sparsely the flowers are distributed upon it, whereas on highly shortened, stump-like axes, the flowers are aggregated into clusters of several pieces.
According to observations by Prof. A. S. Merzhanian, at the terminals of all inflorescence axes, the flowers are typically aggregated into groups consisting of 3 flowers, whereby the central one develops more vigorously than the two marginal ones; if instead of 3 flowers there are 2 flowers at the axis terminal, even in this case one of them is better developed than the second. The total number of flowers per single inflorescence varies extremely widely depending on the cultivar: for instance, in Pinot franc, the inflorescences are small and consist of several dozen flowers, whereas in Saperavi, the inflorescences are very large, ramified, and frequently contain more than a thousand flowers.
