62 



GENERAL REVIEW OV THE ORCHIDEJ;. 



mesophi/ll ; 4, tlie libro-vascular bundle of the midrib : 5, smaller 

 bundles parallel with the midrib (veins) ; G (where present), still 

 smaller bundles (veinlets). The epidermis is always eovered by a 

 structureless cuticle developed from the cell-walls and forming an 

 unbroken layer c)vcr the whole leaf and resisting too rapid evaporation 

 of the fluids within. FiLf. 1 illustrates a transverse section of a leaf of 



Fig. 1. Transverse section of leaf of De/irfcobuiw nohUf at midrib, enlarged 30 diameters. 



1, upper, 2, lower epidermis ; 3, pai'enehyraa or soft tissue containing chlorophyll granules ; 4, fibro- vascular 

 bundle of the midrib ; 5, two smaller bundles. 



Dendrohium nohile enlarged 30 diameters. Immediately underlying the , 

 upper epidermis is a layer of almost circular colourless cells tilled with 

 air or water ; a similar layer of smaller and more closely packed cells 

 underlies the lower epidermis ; the cellular tissue between them consists 

 chiefly of egg-shaped cells filled with gramdes of green colouring matter, j 

 the chlorophyll, not shown in the figure ; they are less closely packed than I 



Fig. 2. Transverse section of fragment of leaf of Dendrohium Jenldmil, X 40. The numerals as in Fig. 1. 



3a, palisade cells. 



(From the Gardeners' Chronicle.) 



the others, and have interspaces here and there between them which 

 communicate with the outer air by means of minute pores or stomata 

 in the epidermis, also not shown in the figure. In the centre is the 

 midrib, and on each side of it a smaller fibro-vascular bundle which 

 contribute to the strengthening of the leaf, passage of fluids, etc. The 



