446 Proceedings of the Royal Irkh Academy. 



from the epidermis by a large celled parenchyma of several layers, 

 and which encloses a central space of parenchymatous tissue. 

 The annular (in transverse section) region of tissue in which the 

 bundles are embedded is lignified. This differentiation into " cor- 

 tical," "woody," and "medullary" regions, is seen still more 

 plainly in the main stem of an inflorescence. The members of this 

 ligneous cylinder (seen as a ring in transverse section) preserve 

 their cell character, and often store up starch. Outside the ligneous 

 cylinder there are no bundles, except just below the insertion of a 

 leaf, where the leaf-traces traverse the cortical tissue, and where a 

 lateral root or axillary bud are found. In the last case most of the 

 bundles coming from the lateral shoot pass through a perforation in 

 the ligneous cylinder and enter into the medullary part. Having 

 traversed this central part for some distance horizontally or obliquely, 

 they fuse with leaf -traces which lie close to the medullary part, but 

 not with the leaf -traces of the subtending leaf. A few bundles also 

 coming from the lateral shoots fuse with small leaf-traces lying on 

 the outer portion of the ligneous cylinder. The bundles of the leaf, 

 which are about seventeen in number, are of two distinct sizes as they 

 enter the stem. The larger bundles enter the ligneous ring at a short 

 distance below the node from which the leaf springs, the smaller bundles 

 somewhat lower down (PL xiv., fig. 29). The latter do not ever enter 

 deeply into the stem, but always remain in outer region of the ligneous 

 ring. As we trace the larger bundles downwards we find that in the 

 stem one becomes considerably larger than the rest. This is the median 

 leaf-trace. Two lateral bundles coming from the leaf, and separated 

 from the median bundle by about 120°, are next in point of size. These 

 three bundles are also distinguished by the fact that as soon as they 

 have entered the ligneous cylinder the central "medullary" portion 

 becomes triradiate in transverse section, and the three rays of " medul- 

 lary " tissue reach out to these bundles. As the bundles slope 

 gradually inwards these rays are shortened. Often in the middle of 

 the internode we find the median bundle fairly far advanced into the 

 medulla and surrounded by a ligneous sheath of fundamental tissue, 

 which is in places disconnected with the ligneous cylinder of the stem. 

 During the course of the leaf-traces in the stem they may become 

 connected with other bundles, either by applying themselves bodily to 

 the other bundle and passing over completely into it, or by being 

 connected to it by a small bundle, while both the bundles which are 

 connected by the smaller bundle still preserve a distinct course. The 

 small connecting bundle is distinguished by the fact that it has almost 



