OctoIxT, I916.] 



THE ORCHID WORLD. 



257 



Fig. 7. Transverse section of leaf of Vanda tricolor at mid rib, x ^10 

 diameters, Nos. 1—5 as before ; 7, bast-like fibres. 



sun, and also ample storage for water. The 

 appearance of isolated bast-like fibre near the 

 upper epidermis is significant of high 

 development. 



In Cypripedmm niveum the layer of long- 

 vertical prism-like cells underlying the 

 epidermis might be mistaken for palisade 



fluid, h'ig. 8, C. insignc closely resembles C. 

 niveum, except that the cells of the mesophyll 

 tissue are more uniform, and the lowermost 

 contain no colouring fluid. Shade and a 

 copious supply of water are the cultural indi- 

 cations to be derived from this structure. 



Stems. — Transverse sections of the stems of 

 Orchids show generally the normal mono- 

 cotyledonous structure. There is a well- 

 marked epidermis consisting in stems of more 

 than one year's duration of closely-packed 

 cells, covered by a hard cuticle more or less 

 thickened ; underlying the epidermis is a belt 

 of corky tissue enclosing the central mass of 

 parenchyma, the cells oT which are soft and 

 thin-walled ; and in the last-named tissue are 

 embedded the fibro-vascular bundles more or 

 less isolated. In addition to these there is in 

 some cases a layer of corky tissue developed 

 between the epidermis and the fundamental 



Fig. 8. Transverse section of leaf of Cypjipeduim iiisigne at the 

 mid-rib, x 25. The niniierals as before. 



structure, but they contain no chlorophyll, and 

 are colourless and filled with water. Beneath 

 them is the chlorophyll layer of ovoid or 

 globular closely packed cells, in the midst of 

 which are the fibro-vascular bundles ; the cells 

 beneath these contain a purplish colouring 



Fig. 9. A fr.igment of transverse section of stem of Dendrobium 

 nobile, enlarged 30 diameters. 1, epidermis ; 2, fibro-vascular 

 bundles ; 3, fundamental tissue. 



tissue, as shown in Figs. 1 1 and 12. Like the 

 fibro-vascular bundles of the leaves those of 

 the stem always consist of at least two 

 elements, one of thin-walled cells called the 

 bast or phloem, and the other, the xylem, of 

 more or less elongated, thick-walled (prosen- 

 chymatous) cells that become hard and 

 ligneous. The bundles of the stems are much 

 more closely packed and usually of larger size 

 than those of the leaves, and fill up a great 

 part of the central mass that is surrounded by 

 the corky tissue and impart to old stems their 

 hard and ligneous texture. In the pseudo- 

 bulbous and swollen stems of many Orchids 



