*نسيج وعائي لحائي*Comprehensive explanation of sieve elements - University of Hamburg Department of Biology*Introduction to secondary phloem tissue by Dr. David T. Webb - University of Hawaii*Katherine Esau (1969).
==See also==*Phloem*Vascular tissue==External links==*Comprehensive explanation of sieve elements - University of Hamburg Department of Biology*Introduction to secondary phloem tissue by Dr. David T. Webb - University of Hawaii==References==*Katherine Esau (1969).