Notes. 
150 
The outer layer, excepting where root-hairs occur, functions as 
a sheath to prevent loss of water ; the inner layer stores up water, 
absorbed by the root-hairs, and passes it on to the passage-cells of the 
exodermis. 
Bromheadia palustris , Lindl. is a terrestrial orchid which lives in 
hot, sunny places, and is rarely found in shady or damp spots. The 
velamen is precisely similar to that of the preceding species, excepting 
that it peels off at once, and its hairs are reduced to thickly cuticu- 
larised papillae which scarcely protrude beyond the other cells. Thus 
there are never any normal root-hairs, acting as absorptive organs. 
Over any definite part of the root, the velamen lasts but little longer 
than the cells of the root-cap. Hence the epidermoidal layer is, 
almost at once, the external layer of the root. For the rest, the 
structure of the root is extremely similar to that of B. alticola. But 
compared with the latter plant the following differences may be noted. 
The cortical cells are longer and have more extensive intercellular 
spaces between them ; in addition there occur little groups of cells, 
similar to the cortical cells of Grammatophyllum , with lignified reticu- 
late thickenings and thin pitted areolae of cellulose. In the vascular 
cylinder the bundles are more numerous, that is, there are more 
numerous radial series of wood-vessels alternating with masses of 
phloem; but the most striking distinction consists in the larger pith 
which is made up of more numerous and larger cells, and has a more 
considerable intercellular system. 
I noted some roots slightly flattened on one side : the vascular 
cylinder was approximated to the same side, and the cortical cells were 
smaller than on the reverse half. Probably this lack of radial sym- 
metry was merely caused by the root coming in contact with a stone 
or some hard object. 
In the cortical cells mycorhiza is present. It does not penetrate 
into the vascular cylinder, nor is it found in the elongated cells of the 
exodermis ; but often a passage-cell contains very thick, yellow, glis- 
tening, mycorhizal hyphae, which can be traced into adjoining cells 
as fine hyphae, and often appear continuous with still finer hyphae 
outside the root. The mycorhiza is not found in the part of the root 
over which the velamen is still present. It is quite possible that this 
is due to the fact that hyphae cannot penetrate the thick outer layer 
of the velamen, in which case the absence of endotrophic mycorhiza in 
B. alticola is easily explained. 
