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



large and angular, are scattered on all sides of the xylem, sometimes appearing in 

 contact with the protoxylem. In longitudinal section they are seen to be short, broad 

 elements with spiral thickenings and bordered pits. In a similar section of the plumular 

 leaf it is interesting to note that the transfusion-tissue is confined to the sides of the 

 bundle ; there are no tracheides opposite the protoxylem, as in the cotyledon. This is 

 what one would expect to find in passing from the more primitive to the more modified 

 organ. 



Libocedrus deciirrens, Torr. — In a transverse section of the cotyledon the transfusion- 

 tissue is seen to extend on all sides of the xylem of the single bundle, and there also 

 appear to be transitional elements between the protoxylem and the transfusion-tissue. 

 In a similar section of the phnmdar leaf the transfusion-tissue is seen to be present only 

 at the sides of the bundle, and entirely absent from the region opposite the protoxylem. 

 In a longitudinal section of the cotyledon it is seen that undoubted transitional stages 

 between the protoxylem and the transfusion-tissue exist opposite the former, consisting 

 of elongated tracheides with both spiral thickenings and bordered pits. To the outside 

 of these the tracheides become shorter and have exclusively bordered pits. On the sides 

 of the bundle the transfusion-tracheides are very much shorter and have either bordered 

 pits or reticulate-spiral thickenings. They are usually greater in diameter than those 

 opposite the protoxylem. In a longitudinal section of the plumular leaf the centripetal 

 xylem, of long elements with reticulate-spiral thickenings, is seen to occur on the ventral 

 side of the protoxylem, and there are transitions from these to the transfusion-tracheides, 

 w^hich are shorter and stouter. 



Juniperus bermudiana, Linn. — In a transverse section of the cotyledon the transfusion- 

 tissue of the small bundle is seen extending from the lateral position round to the ventral 

 side of the protoxylem, where its tracheides are larger and also scarcely lignified ; in 

 some sections they are absent from this part. In a longitudinal section of the cotyledon 

 a vertical row^ of rather short tracheides was observed opposite the protoxylem. In a 

 transverse section of the leaf the transfusion- tissue occurs in a lateral position and is 

 only somewhat inclined towards the ventral side of the xylem, not extending so far 

 round in that direction as is the case in the cotyledon. This is interesting, as showing 

 the gradual modification which has taken place in the more recent organ. 



In the great group of the Abietinege the transfusion-tissue is very characteristic and 

 has been well figured and described by Daguillon *. It consists of tracheides of the usual 

 shape, with very transparent walls and well-defined, circular, bordered pits. These occur 

 in the pericyclic region, and usually extend completely round the bundle, forming a kind 

 of cylinder of transfusion-tissue. In some it is chiefly found around the xylem, in 

 others, again, chiefly around the phloem. Daguillon cites the case of Pinus sylvestris, L., 

 where, in the bundles of the cotyledon, the transfusion-tissue occurs on the ventral side of 

 the xylem, in thQ foliage -leaf on the contrary, chiefly round the phloem. This, again, is 

 a very suggestive and interesting case. In a transverse section of the cotyledon of Finns 



Kev. gen. de Bot. ii. (1890). 



