ME. W. C. WOKSDELL ON " TEANSFUSIOX-TISSUE.*' 313 



side of this, and still directly opposite spiral elements of tlie protoxylem, evident 

 transitional elements are seen which represent centripetal xylem ; these sometimes ahut 

 directly on the protoxylem, in other cases lie a short distance away from the latter. 

 These tracheides are sometimes of great length and quite narrow, having the same sliape 

 as a traclieide of the protoxylem. They possess transitional characters in their walls, 

 where rudimentary bordered pits with wide openings and large borders occurred in the 

 midst of very fine and delicate, but regular and close, spiral or reticulate markings. 

 Fartlier away from the protoxylem, in a radial direction, the tracheides gradually become 

 shorter and stouter, this also happening in a tangential direction towards the sides of 

 the bundle. 



Araucaria imbricata, Pav. — In a transverse section of the leaf a number of small, 

 parallel bundles are seen. At the sides of each bundle well-developed transfusion-tissue 

 occurs ; in many cases it curves round so that a group of its tracheides frequently comes 

 to lie, by itself, opposite some part of the protoxylem ; in such a case the tracheides of 

 the group nearest the protoxylem are smaller than the others. In some cases, directly 

 opposite the main 2)art of the protoxylem, are seen one or two small, round elements of 

 centripetal xylem. They afford a very clear instance of a remnant of this latter tissue 

 (fig. 18). 



Ikimmara sp. — A number of parallel bundles traverse the broad lamina, as in 

 Araucaria. In transverse section the transfusion-tissue is seen to extend on all sides of 

 the xylem, and there are also other smaller tracheides abutting directly on the ventral 

 side of the protoxylem (fig. 19). In longitudinal section one or two of these latter 

 elements are seen to be elongated tracheides with pointed ends and spiral thickenings 

 situated immediately on the ventral side of the elements of the protoxylem with loose 

 spirals. They thus exhibit an undoubted case of centripetal xylem. The transfusion- 

 tiacheides are of quite a different appearance and quite typical in character (fig. 20). 



Sequoia gigantea, Lindl. & Gord. — In a transverse section of the cotyledon the single 

 bundle possesses a very conspicuous development of the secondary centrifugal xylem. 

 Only one or two elements of transfusion-tissue are present at the sides of the bundle. 

 There are no tracheides on the ventral side of the xylem. In a similar section of the 

 foliage-leaf theYe is seen to be a very much smaller amount of secondary centrifugal 

 wood. The transfusion-tissue, on the other hand, has reached a greater development 

 than I have seen in any other Conifer ; its outermost tracheides being of very great 

 diameter, nearly equalling that of the entire xylem of the bundle. The innermost are 

 very much smaller. The nearest approach to centripetal xylem in this plant that I 

 found w^as one of the innermost transfusion-tracheides, smaller than most of the others, 

 which was situated in an intermediate position between these and the protoxylem. 



Widdringtonia Whytei, Rendle. — In a transverse section of the cotyledon the trans- 

 fusion-tracheides, which are of various shapes, both small and rounded and also very 



