Dixon — On the Vegetative Organs of Vanda teres. 455 



to the groups of sieve-tubes in the central cylinder, while opposite to 

 the xylem-rays there are two or three thin -walled passage cells. 

 Immediately within these passage cells are a number of parenchyma- 

 tous cells belonging to the pericycle, and to these the outer tracheal 

 elements of the xylem-ray adjoin. The xylem-ray ends internally in 

 a large vessel surrounded by thickened wood-parenchyma-cells. The 

 xylem-rays are separated from the strands of bast by sclerenchymatous 

 cells. Each strand of bast between the xylem-rays consists of a few 

 (2-5) sieve-tubes, with companion cells, and is usually separated from 

 the sclerenchymatous cells by a layer of thin -walled parenchyma, so 

 that it is uncommon for a sieve-tube to directly come into contact with, 

 a sclerenchymatous cell. The cells of the inner fundamental tissue 

 include small air-spaces, and are strongly thickened. 



The structure of the root apex seems to agree in its general 

 characteristics with that of other aerial roots (cf . Yan Tieghem, Traite 

 de Botanique Edit. 2, p. 695). However, it has one peculiarity which, 

 so far as I know, has not before been described. If a longitudinal 

 section be made of an apex fixed during the resting season of the plant, 

 when its growth is very slow, the outer cells of the root-cap are seen 

 to be covered by a thick cuticle, so that the whole root-cap very strongly 

 resembles a many -layered epidermis, as it is regarded by Van Tieghem 

 {I.e. 696}. If on the other hand the section is made from material 

 fixed in active growth, the outer cells of the root-cap exhibit the usual 

 and collapsed appearance characteristic of this tissue. 



At the point of union of the root, the stem, the usual re-arrangement 

 of tissues found in this position in other monocotyledons is found. If 

 the structure of the root is examined by a series of transverse sections 

 passing up from the apex, this re-arrangement is first found in sections 

 on a level with the outer surface of the petiole through which the 

 root has emerged. Here the cortex is reduced to a few layers in thick- 

 ness, and when traced inwards, is found to merge with the cortical 

 tissue of the stem ; at the same time the endodermis loses its regularity 

 and passes over insensibly into the outer layers of the ligneous cylinder 

 of the stem. The bundles coming from the root, each composed of a 

 single group of xylem and phloem elements, pass into the stem and 

 apply themselves for the most part to the peripheral bundles on that 

 side of the stem in which the root has taken origin. Some of the root- 

 bundles, however, unite with the inner bundles of the stem, and occasio- 

 nally a bundle coming from the root divides into two branches, which 

 fuse Avith distinct leaf-traces in the stem. In no case did I observe a 

 bundle coming from a root to penetrate to the inner or outer Dundles on 



