122 TRANSFUSION-TISSUE IN GYMNOSPERMOUS PLANTS. 
derived from the parenchyma of the ground-tissue of the leaf, or 
even of the pericyclie cells; nor is it, again, as others have 
imagined, the equivalent of a lateral vein or branch of the bundle. 
The conclusion at which I have arrived is that this tissue isa 
direct derivative of the centripetal xylem which normally occurred 
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22 
Fig. 3. Transverse section of vascular bundle of the leaf of Tarus baccata. 
ph-phloem; pr=protoxylem; x'=centripetal xylem ; a? =centtr 
fugal xylem. 
Fig. 4. Longitudinal section of vascular bundle from the leaf of Dammara, and 
two elements of transfusion-tissue. ph=phloem; pz =protoxy len; 
z'=centripetal xylem; 2?=centrifugal xylem; tf = transfusion 
tissue. 
as an important part of the vascular bundle in the ancestors of 
the plants concerned (for which fossil plants afford ample 
evidence). But as, in the course of time, the centripetal xylem 
of the bundle disappeared, as having become a useless tissue, the 
origin of the transfusion-tissue, which has persisted as 2 high 
useful portion of the bundle, has become almost completely 
obscured. 
(The figures illustrating this paper are drawn quite diagram 
matically. At some future time I hope to publish à mor 
detailed investigation of this subject, accompanied by fu" 
elaborated and accurate figures. 
June 15, 1897. w.c. W] 
