Q.Why is the flower regarded as a modified, condensed shoot specialised for sexual reproduction in angiosperms?

In a flower, the internodes of an ordinary vegetative shoot are extremely condensed, and the lateral appendages that would otherwise be leaves are instead modified into the four floral whorls, each specialised for a reproductive role. …

A vegetative shoot has an axis bearing leaves at nodes separated by internodes, and it continues to grow indefinitely at its apex. A flower, by contrast, arises when the shoot apical meristem switches from vegetative to floral development: the internodes between successive whorls become extremely condensed so that calyx, corolla, androecium and gynoecium all appear to arise almost at the same level on a short axis, the thalamus.

Each of these whorls is homologous to a modified leaf, but instead of photosynthesising or supporting vegetative growth, each is dedicated to sexual reproduction: sepals and petals protect the flower and attract pollinators, stamens produce microspores that mature into pollen (the male gametophyte), and carpels enclose the ovules in which the female gametophyte develops. Once its whorls are formed, the shoot's growth is also determinate -- it stops growing further at the apex, unlike a vegetative shoot. …

Compare the flower's structure (condensed axis, modified leaves as whorls, determinate growth) against an ordinary vegetative shoot, then …

Treating the flower as a wholly separate kind of organ rather than a modified shoot; forgetting that its growth is determinate, un …