Plants are placed into two simple kingdom subsections: nonvascular and vascular plants. The big distinction between the two groups is that vascular plants have vascular_tissues: tissues that conduct water and dissolved food in the plant body. The vascular tissues include xylem, which moves water and minerals upward through the plant and phloem, which moves dissolved food downward in the plant.
Nonvascular plants lack these tubes, and therefore must be small and thin so that each cell can acquire its needed materials via passive_transport from the plant's surface, or from other cells within the plant that are located near the surface.
Regardless of whether a plant is vascular or nonvascular, it has structures that (1) anchor it into the soil, (2) provide physical support for its' photosynthetic structures, and (3) specialize in performing photosynthesis.
The difference is that in nonvascular plants these structures are called root-like, stem-like, and leaf-like because they lack vascular tissues. True roots, stems, and leaves are those body structures that contain vascular tissues.
Highly developed vascular systems allow the production of an effective adult plant body, with sufficient reserves to allow the investment in specialized body structures used for reproduction. Good vascularization also provides for structures used to enhance dispersal of the gametes and/or zygotes (fertilized eggs).
Flowers are Angiosperm reproductive organs. Some flowers contain both male and female structures, others have only a single sex. The stamen is the male reproductive organ of a flower and consists of an anther and a filament. The pistil is the female reproductive organ, and consists of the stigma, style and ovary.
Each anther consists of four fused microsporangia, which are known as pollen_sacs. The pollen sacs contain pollen_grains. Pollen grains provide protection for sperm cells. NOTE: the tapetum is a layer of cells that provides the nourishment for developing sperm.
Three pistils are fused together to make up what your authors refer to as the ovary of the Lily. Each pistil is supported by a carpel, which is modified sporophyll_tissue that surrounds the pistil. In the Lily ovary, three carpels are fused together. In some texts, the terms pistil and carpel are used interchangeably.
The pollen grains of the Lily (an Angiosperm) are similar to those of the pine (a Gymnosperm). The tube_cell (which governs production of pollen_tubes) and the generative_cell (which nourishes developing sperm) are visible in most sections.
In the Angiosperms a fruit encloses all seeds. Uneaten fruits provide nutrients to the potential plants they contain. If eaten by animals, fruits may assist with seed dispersal.