350 WILLIS : MORPHOLOGY OF THE PODOSTEMACEÆ 
are often very large — to 1 cm. long — and much branched in 
this species. The drifting part is usually fairly frequently 
branched, the branches also drifting and repeating the 
structure of the original thallus ; the creeping part is less 
often branched. 
The thallus is flattened, but not so much so as in the 
species to be considered below ; at the base it may be as 
much as 4 mm. wide and 3 mm. thick, and tapers to the tip. 
It is not unlike the thallus of Podostemon Barberi, but longer 
and narrower, and in the older parts it grows in thickness 
like the thallus of D. elongata, more especially in the central 
part, while the marginal portions shrivel (PI. XX., fig. 4), 
The vascular strand and the general anatomy of the thallus 
are much as in the preceding species. The secondary shoots 
are about the same distance apart, and the thallus is often 
more or less zigzag, small lateral projections being formed 
under each secondary shoot (PL XX., figs. 3, 5). 
The general structure and history of the secondary shoots 
is the same in all essential features as in D. elongata, and the 
basal third or even half, or more, of the thallus becomes 
ultimately floriferous. The formation of the bracts by the 
metamorphosis of the leaves is clearer in this species than 
in the last, and requires a little explanation, as the method of 
formation is common to other genera of the order, and the 
examination of herbarium material in various stages of the 
metamorphosis has led to many errors and much confusion. 
The figures in PL XX. show the process clearly. In fig. 6 
the secondary shoot is beginning to develop a flower ; it 
still has several long leaves with sheathing bases. The bases 
enlarge, especially those of the two uppermost leaves, and 
the tips of the leaves begin to shrivel as in fig. 7. Then 
follows the stage shown in fig. 8, where the tips have mostly 
fallen away, and finally the process reaches the stage shown 
in fig. 9, where the flower is open, with its spathe split into 
several teeth at the tip ; at the base of the spathe are two large 
more or less cowl-shaped bracts with no tips, and below these 
two or more leaves, which are only little enlarged, but 
