2s8 THE ORCHID WORLD. [October, 1916. 



Fig. 10. Transverbe section of stem of Laelia purpurata, enlarged 

 40 diameters. 



1, epidermis; 2, hypodermal layers of thick-walled cells; 3, funda- 

 mental tissue ; 4, air cavities in the fundamental tissue ; 5, fibre- 

 vascular bundles of wcoly fibres of the stem. 



occur many cells rich m mucilage and others 

 which are especially adapted for the retention 

 of water and as storage for reserve material 

 to be utilised by new growths. 



The general structure of the stems of 

 Orchids will be readily understood from the 

 annexed sections made from four species well 

 known in cultivation. The development of a 



Fig. 11. Fragments of transverse sections of the yoimg stem of 

 Vanda tricolor. 



A, near the apex, with one layer of epidermal cells only. B, 1^ inch 

 below A, showing epidermis with two layers of cells and the com- 

 mencement of the formation of corky tissue. 



1, epidermis; 2. corky tissue developing from fundamental tissue; 

 3, fundamental tissue; 4 and B, bast-'ike cells; 5, fibro-vaseular 

 bundles. 



Fig. 12. Fragment of transverse section of older portion of stem 

 of \'anda tricolor with (2) corky tissue well developed. 4, isolated 

 bast-like cells. 



stem of a monopodial Orchid is shown by 

 transverse sections of the stem of Vanda 

 tricolor (Figs. li and 12) at three successive 

 periods of growth, and to give a clearer idea 

 of the form of the individual cells fragmentary 

 sections both transverse and longitudinal are 

 given of the stem of Cattleya intermedia 

 enlarged 200 diameters (Fig. 13). 



Roots. — The general structure of the roots 

 of Orchids is described under the vegetative 

 organs. As regards the minute struc- 

 ture the main features are the same 

 as those of other monocotyledonous 

 plants. There is (i) an epidermis, 

 not always well defined, and beneath 

 this (2) a band of cortical tissue, 

 which is much more developed in 

 some genera than in others, and in 

 aerial more than in terrestrial roots ; 

 in the former it consists of compara- 

 tively large thin-walled cells filled with 

 water, and often with a fine spiral 

 thread coiled within them. Under- 

 the cortical tissue is a layer of 

 thick-walled cells (3) called the endo- 

 dermis enclosing (4) the fundamental tissue 

 of the root ; and lastly there is (5) the 

 axial cylinder consisting of bast and wood 



lying 



