408 WILLIS : MORPHOLOGY OF THE PODOSTEMACEÆ 
American forms, without much difference from what has 
been described in Tristicha, excepting a reduction of the size 
and complexity of the secondary shoots. 
In the Indian Eupodostemeæ we find the most remarkable 
types of thallus in the order. In Podostemon subulatus the 
thallus arises endogenously from the base of the hypocotyl, 
but is itself exogenously branched, and has a very curious 
collenchymatous and non-deciduous root-cap ; it is still 
thread-like, but is perhaps rather more dorsiventral than 
that of the American Podostemons, and its secondary shoots 
are much smaller. In P. Barberi the dorsiventrality is 
more marked, the thallus being broad and almost leaf-like, 
though it is still attached to the rock in the middle line. 
In the remaining Indian genera, there are several types 
of thallus structure. Thus in Dicræa and Griffithella we 
find the very remarkable alga-like forms above described, 
some of which, e.g.^ the creeping closely -attached forms of 
D. stylosa fucoides and G. Hookeriana Willisiana, are not 
very different from the thallus of Podostemon Barberi ; they 
are endogenously developed from the base of the hypocotyl, 
have very reduced secondary shoots, are exogenously 
branched, markedly dorsiventral in their external and 
internal structure, and have the collenchymatous root-cap. 
From this form it is an easy stage to the more or less freely 
drifting type of thallus found in the same varieties, and to 
the somewhat more modified and slightly dimorphic thalli 
of D. elongata and D. dichotoma or D. stylosa laciniata. 
Even the extraordinary forms found in Griffithella, such as 
the stalked goblet in PI. XXYI., fig. 1, are led up to by easy 
stages through intermediate forms. 
In this connection attention may be specially drawn to 
the remarkable polymorphism exhibited by these thalli, and 
which is well shown in the figures of Plates XXI.-XXVL 
The thalli of many of the other genera are very variable, 
but none approach the wide range of form seen in the thalli 
* Cf. 42, under Ligea, Apinagia, Mourera, Lonchostephus, Marathruui, 
Podostemon, Mniopsis, &;c. 
