337 
and its Mycorhiza. 
Dictyostega orobanchoides (Burmanniaceae) the leaves of the 
rhizome do produce absorbing hairs and form the absorptive 
organs of the plant. 
There is a third possibility, namely, that the vegetative 
axis is a rhizome in which the leaves have been completely 
suppressed. I have already shown that in a hemisaprophytic 
Orchid ( Corysanthes ) there is an atrophy in the leaves of the 
absorbing rhizome. In a later paper I shall show that the 
same atrophy has taken place in the green Burmanniaceae to 
such an extent that the leaves are mere microscopical scales 
(cp. Psilotum). Further, the structure of the stele in absorbing 
rhizome-axes of hemi- and holo-saprophytes is frequently 
remarkably like that of a root ( Corysanthes , Burmannia , 
Corallorhiza :), so the root-like nature of the stele of the absorb- 
ing organ is no proof of its root-nature. Nor is the position 
of the spiral and annular vessels absolute testimony that it is 
a root, for even in the inflorescence-axis of Thismia the proto- 
xylem is not accurately radially within the phloem and later 
wood ; and in indubitably absorbing stems of saprophytes, 
the protoxylem often does not stand radially within the later 
formed xylem. 
The fact that in some other Burmanniaceae the rhizome 
develops as an absorbing organ, is not of the slightest value 
as evidence that the absorbing vegetative axis of Thismia is 
really a rhizome. For amongst the Orchidaceae in some 
forms the root-system is entirely absent and the rhizome 
greatly developed as an absorbing and vegetative organ 
(. Epipogum , Corallorhiza :), whereas in other Orchids the roots 
are greatly developed and act as absorbing organs ( Galeola 
javanica , Neottia , &c.). 
But the structure of the growing-point, taken together with 
that of the stele, seems to me to point rather to the absorbing 
organ being a root, and not, as hitherto assumed, a rhizome 1 . 
However, it seems safer to call it a thallus. 
1 See Engler, Burmanniaceae, in Engler & Prantl’s Pflanzenfamilien. 
