transfusion tissue

The tissue immediately surrounding at least part of the vascular bundles in the leaves of gymno-sperms, e.g. Pinus. Transfusion tissue is composed of tracheids (transfusion tracheids) with conspicuous *bordered pits , and parenchyma cells (transfusion parenchyma) containing tannin-like substances and sometimes starch. The main function of the transfusion tissue is believed to be the transport of materials between the vascular bundles and the mesophyll.