DR KEITH WHEELER / SCIENCE PHOTO LIBRARY DR KEITH WHEELER / SCIENCE PHOTO LIBRARY
Phloem plant cells. Light micrograph of a longitudinal section through phloem tissue in a Cucurbita plant. Most of this tissue is large phloem tubes (stained blue). At far right is some parenchyma tissue. The phloem sieve tubes are made up of lines of sieve members. Each sieve member has sieve plates at either end (dark green blue). The sieve plates have primary pit fields with canals (plasmodesmata) through which pass protoplasmic strands surrounded by callose (blue). Magnification: x100 when printed at 10 centimetres high.
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