12 Tans ley and Chick . — Notes on the 
fan-shaped frond, and this has a bulky band-shaped strand 
(Fig. i o), while that of the rhizome is much smaller. As in 
P allavicinia. decipiens , and apparently all such cases, the stalk 
of the frond is a direct continuation of the rhizome-axis, the 
rhizome itself being a sympodium, and the strand of each 
new member of this being discontinuous with that of the last. 
The base of the new strand is particularly weak, and it 
becomes gradually stronger as it passes up to the base of 
its frond-stalk. 
We think it will be admitted that the facts support in 
a general way the theory of the water-conducting function of 
these strands, a bulkier strand being found wherever the axis 
can no longer depend directly on absorption by rhizoids. 
Before we leave the Liverworts, we may refer to the 
striking absence, so far as is known, of anything like a water- 
conducting system among the very numerous and successful 
leafy Jungermanniaceae, the external vegetative organs of 
which are often so highly developed. The general explana- 
tion probably lies in the fact that practically all these forms 
are accustomed to absorb water at all points of their surface, 
which, owing to the great division of the body into leaves and 
leaf-lobes, is very much greater, compared with the mass of 
the plant, than in the thalloid forms. We even find the same 
thing among many of the Mosses in which no water channels 
exist. As Haberlandt 1 has pointed out, such forms are either 
hydrophilous or xerophilous ; in either case absorbing water 
over the whole surface when they do absorb it. It may be 
laid down as a general principle, in fact, that a specialized 
water- conducting channel is as a rule only developed where 
the region of absorption is localized. 
There is, however, in at least one genus of the leafy Liver- 
worts, and probably in others, an indication of the develop- 
ment of the other great form of conducting channel, which 
provides for the passage of formed food-substances. The 
case to which we allude is the strand of elongated cells 
forming a kind of 4 midrib,’ though only one cell thick, in the 
1 Beitrage, pp. 389-91. 
