I 



Dixon — On the Vegetative Organs of Vanda teres. 447 



no sclerenchymatoiis sheath. The three large bundles of the leaf are 

 subject to connexions of this last kind only in the first internode. 

 Most, if not all the other bundles, unite completely with other bun- 

 dles in the first internode. Some of these fusions take place, contrary 

 to what is generally stated for monocotyledons, in the inner parts of 

 the stem. The two small bundles at either side of the median leaf- 

 trace are connected with other bundles only near the base of the first 

 internode. The three large leaf-traces which run in the segment of 

 the stem between the two large lateral leaf-traces fuse with other 

 bundles, which are about equal to them in size, shortly after they 

 reach the inner region of the ligneous ring. Sometimes a small 

 bundle in the periphery of the ligneous ring, when traced downwards, 

 comes to an end in the ligneous tissue surrounding it. PL xiii., 

 fig. 16, shows a cross section of such an ending, and PI. xiii., fig. 15, 

 is drawn from the last section in which this bundle was trace- 

 able. 



The bundles running in the " medulla " are limited usually to two- 

 or three, and these are generally in connection with the axillary buds. 

 Sometimes, however, one of the large leaf-traces is connected with 

 another leaf-trace by a small bundle, which runs inwards from the latter 

 trace into the medulla, and passes up in this region till it unites with 

 the large trace. In the course of the connecting bundle inwards 

 towards the medulla it may fuse with a similar bundle coming from 

 another leaf -trace. During the course of the small connecting bundles 

 they are often subject to a displacement of their tracheal and criblal 

 portions relatively to one another. In this displacement the sieve- 

 portion may traverse 180° in a horizontal circle. 



The arrangement of the wood of the three large leaf -traces remains 

 in the first internode of their course more or less distinctive. The 

 vessels, three or four in number, are arranged along a radius, the 

 largest being towards the periphery. On each side of the radial plate 

 of vessels there is usually a single layer of wood parenchyma. The 

 bast of these bundles consists of a few sieve-tubes and companion cells. 

 On the outside of the bundle there is a relatively small sclerenchyma- 

 tous sheath, and in this way these are very different in appearance from 

 some of the vascular bundles in the outer parts, which, although com- 

 posed of only one or two sieve-tubes, and a few tracheae, have sheaths 

 which are much stronger than those of these larger bundles. The fibres 

 which form this sclerenchymatous sheath have often exceedingly thick 

 and pitted walls. Along the outer sclerenchymatous fibres of at least 

 the medium leaf-trace, for some distance below the node, are found 



