Vascular is a scientific classification of members of the kingdom Plantae. A vascular plants uses wood or woody tissues to transport water and nutrients throughout the plant's body. The vascular system is composed of elements like leaves, roots and stems. Almost all plants you see on a daily basis are vascular; trees, flowers and grass are all vascular plants.
Vascular tissue is composed of primarily of two components, xylem and phleom, which are what make vascular plants unique. All the vascular tissue in the plant makes up the plant's vascular system.
The best known xylem tissue is wood and it's purpose is moving water throughout the vascular system of the plant. Xylem sap flows through the vascular system distributing water throughout the plant. The sap flows as a result of two processes: transpiration pull and root pressure. Transpiration pull occurs as a result of surface tension created by water evaporating. The water creates microscopic curves called menisci. The menisci create tension in the xylem which causes water to be drawn up from the roots and the soil. Root pressure occurs when the soil around the roots has high levels of solutes. As the roots absorb more liquid through osmosis, an upward pressure is created, allowing the liquids to move through the plant.
Phloem is the tissue that transports nutrients, primarily in the form of sucrose, throughout the vascular system. In trees phloem is the innermost part of the bark. Translocation, the movement of the nutrients created by photosynthesis, is produced by the phloem. Phloem is composed of several kinds of specialized cells, including sieve tubes and companion cells. Sieve tubes are structured without a nucleus and when stacked end to end form tubes that conduct materials throughout the plant. The walls of the cells have pores called sieve plates. The much smaller companion cells carry out many of the cellular functions of the sieve tubes. Companion cells have a higher concentration of ribosomes and mitochondria compared to typical plant cells. The companion cells create smooth surfaces along the sieve cell tubes and certain ones specialize in moving solutes that require more energy to transfer.
The primary distinguishing feature of a non-vascular plant is the absence of the vascular system. Because of this they lack roots, stems and leaves, but many still have tissues designed to transport water and nutrients. Common examples of non-vascular plants are mosses, liverworts and hornworts.
Advantages of the Vascular system
Because of their vascular system, vascular plants have been able to evolve into much larger organisms than non-vascular plants. Non-vascular plants are restricted to a much smaller size due to the lack of tissues specializing in the distribution of nutrients.