Transfusion tissue in gymnosperm leaves

Abstract

Transfusion tissue is universal in leaves of gymnosperms. It is composed of three kinds of cells: thick walled tracheids, parenchyma and albuminous cells. In this paper a comparative account is given of transfusion tissue in 82 species. Differences in transfusion tissue can be classified into 7 groups according to the distribution pattern of tracheids, the different characteristics of secondary walls and in some cases the occurrence of accessory transfusion tissue. The groups are: Pinus-type; Pseudotsuga-type; Tsuga-type; Cupressus-type; Texas-type; Araucaria-type, and Cycas-type. The phylogenetic relationships of various taxa of gymnosperms is discussed on the basis of these different kinds of transfusion tissue. Brief remarks on transfusion parenchyma, sclerenchyma and accessory transfusion tissue are also given.