<P> Sieve elements are specialized cells that are important for the function of phloem, which is highly organized tissue that transports organic compounds made during photosynthesis . Sieve elements are the major conducting cells in phloem . Conducting cells aid in transport of molecules especially for long - distance signaling . In plant anatomy, there are two main types of sieve elements which are sieve cells and sieve tube members . Sieve cells are specialized cells in the phloem tissue of flowering plants . Companion cells and Sieve cells originate from meristems, which are tissues that actively divide throughout a plant's lifetime . They are similar to the development of xylem, a water conducting cells in plants whose main function is also transportation in the plant vascular system . Sieve elements' major function includes transporting sugars over long distance through plants by acting as a channel . Sieve elements elongate cells containing sieve areas on their walls . Pores on sieve areas allow for cytoplasmic connections to neighboring cells, which allows for the movement of photosynthetic material and other organic molecules necessary for tissue function . Structurally, they are elongated and parallel to the organ or tissue that they are located in . Sieve elements typically lack a nucleus and contain none to a very few amount of ribosomes . The two types of sieve elements, sieve tube members and sieve cells, have different structure . Sieve tube members are shorter and wider with greater area for nutrient transport while sieve cells tend to be longer and narrower with smaller area for nutrient transport . Although the function of both of these kinds of sieve elements is the same, sieve cells are found in gymnosperms, non-flowering vascular plants, while sieve tube members are found in angiosperms, flowering vascular plants . </P> <Table> <Tr> <Td> </Td> <Td> This article includes a list of references, but its sources remain unclear because it has insufficient inline citations . Please help to improve this article by introducing more precise citations . (May 2015) (Learn how and when to remove this template message) </Td> </Tr> </Table>

Which of the following structures lies between sieve-tube members in phloem