OF CEYLON AND INDIA. 
857 
slightly upcnrved at the edges. On the lower side haptera 
and rhizoids are formed in the usual way. The next stage 
is seen in August and September, Avhen plants are found 
like that shown in PI. XXII., fig. 3, a few inches across, 
starting at the base from a stout hapterous foot like tliat of 
D. Wallichii, and shown in section in fig. 4. From this the 
thaPus grows outwards and usually slightly upwards, and is 
perhaps most often only attached at the foot, but very com- 
monly also at one or more outer points, usually by haptera, 
but sometimes it is found touching the rock and fastened by 
root-hairs. Sometimes the thallus is entirely prostrate and 
creeping, attached to the rock at all points, and then looks 
just like that of Griffithella, shown in PI. XXV., fig. 1. I 
have not been able to determine satisfactorily what causes 
one form or habit to be assumed rather than another, but it 
seems fairly clear that the fully creeping form is rare, except 
when there is ample space available. When the plants are 
crowded they tend to grow more upwards, attached only by 
the feet. When they grow near the edge of a rock the plants 
tend to give off streaming thalli like those of D. stylosa 
laciniata, but broader. When fully grown the plant may 
reach 20 cm. or more, with the thalli frequently branched or 
lobed ; the lobes are exogenously formed and are often 
as much as 7-10 mm. wide. At the same time they are also 
commonly more or less undulate in form, with margins 
curved up and down, and the whole plant, Avith its red or 
olive colour, has an extraordinary resemblance to a 
Fucus or similar alga, especially Avhen a large mass of 
the form attached only by the foot is found groAving 
together. 
The groAving point is rounded and rather upcnrved at the 
tip, on Avhich is a root-cap almost completely on the upper 
side, as already described by Warming for this species (cf. 
PI. XXII., fig. 6). As seen in section (fig. 5) this develops 
from the meristem. at the apex in the usual Avay, and the 
same meristem. gives rise to the general tissues of the thallus. 
Details need not be given here. At the sides of the groAving 
