1. Behnke, H.D.: Companion cells and transfer cells. In: Phloem Transport (NATO Advanced Study Institute on Phloem Transport), pp. 153?175, Aronoff, S., Gorham, P.R., Srivastava, L.M., Swanson, C.A., eds.. New York: Plenum Press 1975
2. Bentwood, B.J., Cronshaw, J.: Biochemistry and cytochemical localization of acid phosphatase in the phloem of Nicotiana tabacum. Planta 130, 97?104 (1976)
3. Cattesson, A.: Observations cytochemiques sur les tubes criblés de quelques angiospermes. J. Microscopie 16, 95?104 (1973)
4. Crafts, A.S., Crisp, C.E.: Phloem transport in plants. San Francisco: Freeman 1971
5. 30th Ann. Proc. Electron Microscopy Soc. Amer., Los Angeles, Cal., USA;J. Cronshaw,1972