148 
Notes. 
retained, but is evenly strongly developed under the soil : nor does 
the plant Jose its epiphytic habit of giving off negatively geotropic 
roots. This case proves how readily an orchid, like Epidendrum 
cinnabarinum , could have given up its former epiphytic habits, with- 
out at the same time losing its velamen, or even parting with the 
tufts of aerial roots which it still bears. 
Bromheadia *. 
The Malayan genus Bromheadia includes four species, of which two 
are epiphytic and two terrestrial. The epiphytic species are advanced 
representatives of their kind, in that they are lovers of intense light 
and grow at the tops of very tall trees (Dipterocarps), where many 
epiphytes would find existence impossible. Hence, any structural 
differences in the roots of the terrestrial and those of the epiphytic 
species, will throw more light on the effect of an aerial mode of life 
than would be the case if the epiphytic species lived in a semi- 
terrestrial position, such as in the moist, earth- and humus-filled 
pockets formed by the persistent leaf-sheaths of Palms. 
Bromheadia alticola, Ridl. lives in the full blaze of the sun on high 
tree-tops. The plant from which I obtained my material grows on 
a tree-stump in the Botanic Gardens at Singapore. Its long aerial 
roots are brown in colour and feel rough when the hand is passed 
over them : they cling fast to the supporting tree. The root is 
enveloped with a velamen consisting of two layers of cells. The 
cells of the outer layer have highly suberised walls, and their inner 
walls are immensely thickened and traversed by pore-canals. But 
some of the outer cells grow out into root-hairs which, in regions not 
in contact with the support, are short, thickly cuticularised papillae. 
On the ventral side (i. e. in contact with the supporting tree) the hairs 
are long ; of these hairs those nearest the dorsal side are long, thick- 
walled, and highly suberised, so that they only function as organs for 
fixing the root to the substratum ; the rest of the ventral root-hairs 
have thin, slightly cuticularised walls, and flattened or lobed ends : 
according as the root is nearer to, or farther from, the actual surface 
of the substratum, the hairs are longer or shorter. The basal walls 
of the hairs are copiously pitted, obviously in order to permit the 
inward passage of liquids. Fungal hyphae permeate the outer layer 
1 H. N. Ridley, The genus Bromheadia , Linn. Soc. Journ. XXVIII, 1891. 
