301 1 



VIII. On " Transfusion-tissue " ; ity Origin and Function in the Leaves of Gymno- 

 spermous Tlants. By W. C. Worsdell. {Communicated by D. H. Scott, Ph.D., 

 F.R.S., F.L.S., Hon. Keeper of the Jodrell Laboratory, Royal Gai^dena, Kew.) 



(Plates XXIII.-XXVI.) 



Read 4th November, 1897. 



X HIS paper, which has been preceded by a short preliminary thesis, presenting only 

 the chief facts (Journ. Linn. Soc, Bot. vol. xxxiii. pp. 118-123), furnishes a more detailed 

 and elaborate account of the subject therein dealt with. It treats at some length of the 

 origin and distribution of transfusion-tissue in the foliar organs of Gymnospermous 

 plants. 



This tissue is well known to be universally present in the leaves of Conifers ; it occurs 

 generally in the leaves of Cycads, and in those of Ephedra and Welwitschia among tlie 

 Gnetacese. Among Angiospermous plants it is known to occur here and there in leaves 

 and stems, but in these cases in a more or less modified form. 



No one, however, as yet, has been able to give a satisfactory account of the origin and 

 homology of this important and striking tissue. This I hope to be able to do in the 

 following pages. 



Historical Survey. 



The first discoverer of " transfusion-tissue " was the German botanist Frank, who, in 

 an important paper*, describes it in connection with the vascular bundle of the leaf of 

 Taxus baccatay Linn. As regards its origin, he considers it to arise from the bundle, 

 having noticed transitions in the shape and size of the tracheides from the ordinary 

 xylem of the bundle outward to the transfusion-tissue at its side. 



Thomas f mentions transfusion -tissue in the leaves of three genera of Conifers. He 

 believes it to be parenchymatous in origin. 



A paper by Kraus t, " Ueber den Bau der Cycadeenfiedern," dealing with the minute 

 structure of the leaves of various Cycadean genera, does not mention the transfusion- 

 tissue proper, but describes, in the genus Cycas (probably for the first time), the 

 tracheides of the *' accessory transfusion-tissue " running at right angles to the midrib 

 towards the margin of the leaf, and which are characteristic of, and peculiar to, this 



genus. 



In 1871 Mohl published an interesting paper § on the structure and morphology 



'*■ " Ein Beitrag zur Kenntniss der Gefessbiindel," Bot. Zeit. 1864. 



t " Zur vergl. Anat. d. Coniferen Laubblattcr," Pringsh. Jahrb. Band iv. 1865. 



t Pringsh, Jahrb. 1865. 



§ " Morph. Betrachtung der Blatter von Sciadopitys" Bot. Zeit. 1871. 



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