372 WILLIS : MORPHOLOGY OF THE PODOSTEMACEÆ 
slightly asymmetrically placed as in Hydrobryum oliva- 
ceum, and the anatomy of the tissues is also very similar to 
that seen in the latter plant. There is a broad parenchy- 
matous cortex, without any sheath of collenchyma round the 
bundle. The vascular strand itself is made up of groups 
of phloem-like tissue, divided by strands of long parenchy- 
matous cells ; the groups are like those in the thallus of 
Dicræa, and probably arise in the same way. 
At the base of this axis is the thallus, which is com- 
paratively very small ; it is crustaceous, like that presently 
to be described in Hydrobryum, closely creeping, and 
attached to the rock at all points. It is very difficult to make 
out its mode of growth in the mature specimens, but it 
appears to resemble that of Hydrobryum, and the thallus 
is lobed like that of H. olivaceum. It bears (PI. XXX., fig. 
1) numerous closely crowded secondary endogenous shoots, 
which have already been mentioned as forming the most 
striking character of this plant. These may be seen in all 
stages, from very young ones just emerging from the thallus 
up to fully formed flowering or fruiting stalks. 
I have been unable to make out in what order or arrange- 
ment the secondary shoots are developed upon the thallus. 
The lobes of the thallus are very irregular, and very com- 
monly there is a single line of secondary shoots along each, 
but I am inclined to think that the original origin of the 
shoots is rather more marginal than central. 
Beddome, who first described this plant, figures it as 
having two kinds of secondary shoots, the one such as we 
have described, and the other purely vegetative, with 
tetrastichous leaves without sheathing scales. Further in- 
vestigation is very much required at early periods in the 
life-history to determine the exact phenomena, and whether 
all the secondary shoots are at first like the latter type. 
Towards the end of the season most of the still submerged 
secondary shoots bear scales on their whole length, but near 
the top, as Beddome has also figured, these scales bear long 
deciduous loriform green assimilating tips which drift out 
