6i 



GENERAL REVIEW OF TITE ORCHIDE.'E. 



sections uf a leaf and slcui df anutluT two-leaved Cattleya, C velutina, 



proved to l)e nearly identical in structure with those of 0. intermedia. 



Fi<;. 4, Caftlcya Momw. Here the miunte structure is more elaborate, 



Transverse section of leaf of Cattleija Mosske at the midrib. 



1, upper, 2, lower epidermis ; 3, parenchyma or soft tissue of the leaf sometimes called the mesophyll, con- 

 taining chlorophyll granules (not shown in figure); the layer immediately under the upper epidermis indicated 

 by 3a and called the hypoderm, consists of colourless cells containing water; 4, air cavities; 5, fibro- vascular 

 bundle of midrib shown diagramatically, the upper club-shaped portion consists of thick woody cells which 

 serve to protect the more delicate tissue beneath ; tj, smaller bundles (veins), running parallel with the midrib; 



7, still smaller bundles (veinlets). 



presumably indicative of the more changeable climatic conditions under 

 which the plant grows. The leaf is thick and fleshy, the epidermal cells 

 small and closely packed ; the hypoderm or water cells ai'e large ; the 



Fig. 5. Fragment of epidermis and underlying cells of Cattleya Mossiw magnified 200 diameters ; the outer 

 iurface of the epidermal cells is developed into a thick cuticular layer (a) covering the whole surface and 

 which has a peculiar striated structure in the external half This thick cuticle impedes excessive evaporation 



air cavities are also large and nearly equidistant from both surfaces ; 

 the fibro-vascular bundles are numerous and somewhat similarly grouped 

 on each side of the principal or midrib-bundle. This structure may be 



