302 ME. W. C. WOESDELL ON " TEANSFUSION-TISSUE." 



of the leaf of Sciadopitys. He is the first author to use the word " transfusion-tissue," 

 applying it to the tracheides found in the tissue around the xylem of the bundle in this 

 plant. He agrees with Thomas that it belongs to the parenchymatous tissue of the leaf, 

 and not to the bundle. 



Bertrand *, in a general sketch of the anatomy of the stems and leaves in the Gnetaceae 

 and Coniferse, describes and figures transfusion-tissue in several genera, but does not 

 enter into mu.ch detail concerning it. 



De Bary f afi^ords us the completest and clearest account given by any author of the 

 transfusion-tissue as it occurs in the leaves of Gymnosperms, and illustrates his description 

 by two very good figures of leaf-bundles of Cunninghamia and Juniperus communis, Linn. 

 He does not attempt, however, to explain its origin. 



Zimmermann's description % of transfusion-tissue is one of the best and fullest. He 

 rightly argues that a sharp distmction must be made between the large elongated 

 tracheides running out to the margin of the leaf in Cycas and Podocarpus (which are 

 specially modified from the parenchyma) and the real transfusion-tissue at the side of 

 the bundle. 



There is an excellent paper by Scheit §, entitled " Die Tracheidensaume der Blatt- 

 biindel der Coniferen," which is w^orthy of special notice. He made a minute investi- 

 gation into the character of tlie bordered pits and thickenings of the tracheides of the 

 trans fusion- tissue in many genera of Coniferge. Of the transfusion-tissue of the Cycadeae 

 he does not say much, but finds it to agree entirely in most points with that of the 

 Coniferae, He makes an interesting study, with regard to this tissue, of the Gnetaceae. 

 He regards the reticulate venation of the foliage-leaf of Gnetum as a transition between 

 the rudimentary venation of Ephedra and Conifers and the complex venation of Dicoty- 

 ledons. But it Ls very questionable whether he is right in regarding the short tracheides 

 which occur at the point of branching of the bundles and at their final endings as 

 equivalent to the transfusion -tissue of Coniferse. It is, however, of the greatest interest 

 to find that the bracts of Gnetum Gnemon, Linn., which externally resemble the foliage- 

 leaves of Ephedra, have the same rudimentary venation (though here consisting of live 

 to six bundles), and also well-developed transfusion-tissue accompanying the bundles. 

 He appears to be the first author to thoroughly investigate transfusion-tissue from the 

 physiological point of view. At the opening of the paper the tracheidal nature of its 

 elements, ascertained by reference to their mode of thickening, watery contents, and the 

 closed character of the bordered pits, is fully discussed ; at the close he considers the factors 

 which determine the mode of thickening of the transfusion-tracheides and the development 

 of the tissue as a whole. The chief factor determining the character of the wall appears 

 to be the greater or less exposure to the turgescence of the surrounding parencliyma- 

 cells ; in the former case reticulate and other thickenings are present on the wall, in 



* ' Bibliothcque de I'Ecole des Hautes Etudes,' tome xii., art. no. 1, 1875. 

 t 'Comp. Anat. of Phauerog. and Perns,' p. '680, 1877 (Engl. ed. 1884). 

 t " Ueber das Transfusionsgewebe," Flora, 1880. 

 § Jenaiache Zeitschr, f. Naturwiss., Band xvi. 1883. 



