312 MR. W. C. WOESDELL ON '• TEANSFUSION-TISSUE." 



large-celled transfusion-tissue occurring chiefly at the sides of the bundle, but also very 

 frequently indeed on the ventral side of the xylem. A longitudinal section showed 

 that the tracheides of the transfusion-tissue, both at the sides of the bundle and on its 

 ventral side, were of various lengths, some being very long, others shorter ; there is also 

 considerable variation in their breadth, which is usually rather great. Here and there 

 very long and comparatively narrow ones occur opposite the protoxylem, though not 

 directly opposite its main part where the annular vessels occur. In one place, however, 

 opposite such an annular vessel, a short, broad tracheide was observed. The parenchy- 

 matous elements immediately abutting on the protoxylem are, many of them, extremely 

 narrow and of great length, tapering very much at the ends, owing to their having 

 undergone a great amount of sliding-growth. The pitting of the tracheides of the 

 transfusion-tissue and centripetal xylem is very interesting. These elements, at least 

 those on the ventral side of the xylem, have very much the appearance of thin-walled 

 sclerotic cells, and are in many cases almost, if not quite, indistinguishable therefrom, 

 owing to the fact that the pits of many appear to be quite simple. It appears that a 

 degeneration of the bordered pits has taken place such that the borders have become 

 gradually obliterated, so that in most cases only a slight swelling of the wall around the 

 pit has remained (PI. XXVI. fig. 17). This slight thickening can be readily seen both in 

 a sectional and a surface view of the wall. It is in some cases much more distinct than 

 in others, and in such a definite border is seen. It is by means of these latter transitional 

 cases that the real tracheidal nature of all these elements can be determined, and also 

 that none of them are sclerotic cells. The cross-walls are often horizontal, but also very 

 frequently rather oblique. I think there is but little doubt that these tracheides have 

 all been derived from the centripetal xylem which once existed in normal form in the 

 position in which these tracheides now occur, and that the latter have been since 

 extremely modified. 



Aimucaria Bidicillii, Hook. — In a transverse section of the cotyledon the bundles are 

 seen to be united into long bands. There is a great development of transfusion-tissue 

 consisting of elements of various shapes, rounded or angular, reticulated or pitted, often 

 of considerable size, on the ventral side of the protoxylem and immediately abutting on 

 it ; they may also be seen running out into the parenchyma. There are sometimes 

 smaller tracheides next the protoxylem, which arc rounded and appear like normal 

 tracheides of the bundle, though larger. These constitute the centripetal xylem. 



In a transverse section of the leaf a number of parallel bundles are observed 

 traversing the broad lamina. Each of these has transfusion-tissue largely developed on 

 all sides of the xylem, consisting of wide, angular tracheides with small bordered pits. 

 But, abutting on the protoxylem, and connecting the latter with these large tracheides, 

 are smaller ones with rounder, smoother walls, forming a transition between the proto- 

 xylem and the transfusion-tissue, and evidently representing centripetal xylem. In 

 longitudinal section of the leaf there are no transitional elements between protoxylem 

 and transfusion-tissue in direct connection with the main part of the former, i. e. where 

 the elejnents with annuli and long-drawn-out spirals are situated. But a little to the 



