310 ME. W. C. WOESDELL ON " TEANSFUSIOX-TISSUE." 



large round tracheides, the smaller of which lie towards the protoxylem of the bundle. 

 This protoxylem stretches right across the intervening space between the centrifugal and 

 centripetal parts of the xylem, the latter tissue having even some protoxylem elements, 

 attached to it (PL XXV. fig. 13). The centrifugal xylem has a fair development, an 

 active cambium being present. This bundle is therefore extremely interesting as forming 

 in its structure a connecting-link between that of the cotyledonary bundles of Ginkgo 

 and of other Coniferse. 



Cephalotaxiis Fortuni, Hook. — In the cotyledon and leaf, as seen in transverse section, 

 the transfusion-tissue, as in all Coniferse, is very well developed at the sides of the 

 bundle ; but in addition to this, there are nearly always a variable number of tracheides 

 of much smaller diameter on the ventral side of the xylem. They lie scattered, in 

 various positions, among the parenchyma-cells of this region, and are quite distinct and 

 separate from either the protoxylem or the transfusion-tissue. In longitudinal section 

 of the bundle these tracheides are very clearly shown on its ventral side, directly opposite 

 the oldest, spiral elements of the protoxylem, and separated from these by one, two, or 

 three layers of cells. In shape they are somewhat elongated, with square or tapering 

 ends, and reticulate thickenings, with or without bordered pits, on their walls (fig. 14) ; 

 those nearest the protoxylem have reticulations alone, those farthest away in the ventral 

 direction have bordered pits intercalated between the thickenings. These tracheides, 

 seen thus in both sections, as in the above species, are constituents of the centripetal 

 xylem and equivalent to the tracheides observed on the ventral side of the bundle 

 in both the cotyledon and leaf of Ginkgo. 



Taxus (2 species). — In the cotyledon and leaf I was able to discover similar tracheides, 

 though they appeared in this genus scarcely so conspicuous as in Cephalotaxus. These 

 elements, of which, in one transverse section, I observed three, were separated from the 

 protoxylem (whose limit on the ventral side w^as well defined) by a single layer of cells. 

 From their superiority in size to the elements of the protoxylem they could not possibly 

 be outlying members of that tissue. The finely-developed transfusion-tissue at the side 

 of the bundle showed in places an interesting transition in the size of its elements from 

 its extreme outer side, where the tracheides were large in diameter and conspicuously 

 pitted, to its innermost part, nearest the protoxylem, where the final tracheide, in one 

 instance observed, much resembled, in size and in the character of the wall, the elements 

 of the centripetal xylem above-mentioned (fig. 15). In longitudinal section of a leaf- 

 bundle short, reticulate tracheides were observed here and there on the ventral side of 

 the protoxylem, which appeared to occupy the same position with regard to the latter 

 tissue as did those seen in transverse section ; they were also of about the same diameter. 

 Thus in the leaf of this plant also we find a conspicuous instance of centripetal xylem. 



Todocarpiis chilina, Rich. — This plant has long, pointed, and rather broad leaves, 

 provided with a single median vein or midrib. At the side of this bundle the normal 

 transfusion-tissue is remarkably conspicuous, constituting a group of large, pitted 

 tracheides (tig. 16). In a horizontal section of the leaf, i. e. one made parallel to its 



