单语范例（未经PONS编辑处理）
The companion cells, connected to the sieve tubes via plasmodesmata, are responsible for loading the phloem with sugars.
en.wikipedia.org Infection and death of the phloem effectively girdles the tree and stops the flow of water and nutrients.
en.wikipedia.org It feeds on the phloem of different trees, such as lime trees, oaks, maples, birches, elms and hazels.
en.wikipedia.org Polyhedral particles are of 65 nm diameter in the cytoplasm of phloem cells were always associated with the disease.
en.wikipedia.org Those symptoms are related to callose deposition at the sieve plates and subsequent degeneration of the phloem.
en.wikipedia.org