OP CEYLON AND INDIA. 
):);■) 5 
rarel}^ with Lawia zej- lanica. It grows iu rapid water which 
Avhen shallow is liable to be broken, and lives at a rather 
greater average depth than some ot the other forms. 
Dry Season A'lipearance . — In general this is almost 
exactly like that of D. dichotoma, flat, narrow, prostrate 
thalli, with erect fruit stalks. 
Life History and Mature Structure , — In consequence of 
the infrequent flowering of this species, and the somewhat 
awkward places which it mostly affects at Hakinda, I have 
not been able to obtain seedlings ; probably the early stages 
are like those of D. elongata, which the plant resembles very 
closely in habit. When fully grown it is about the same size 
as D. elongata, with prostrate creeping thalli upon the rocks, 
giving off long drifting thalli, often as much as 50 cm, long, 
and sparingly branched. The chief distinction in habit from 
D. elongata is that the thalli are flattened, like very narrow 
ribbons, just like those of D. dichotoma ; they are, how- 
ever. much longer than those of the latter species. 
The thallus has a growing point like that of D. elongata, 
but flattened and broader (PI. XXII., fig. 1), with the 
secondary shoots developing on the upper 'sides of the mar- 
gins in the usual way. The upper side, near to the tip, is 
very convex, the lower approximately flat with a slight 
convexity over the central part, in which the vascular strand 
is situated. The internal structure is much like that of the 
species already described. Subsequently the thallus grows 
in thickness, much as in var. fucoides, described below, by 
meristematic activity in the central part above, and still more 
below, the vascular bundle, while the marginal portions do 
not grow to correspond. In this way the centre becomes a 
stout rib, very prominent on the lower side. The vascular 
bundle is like that of D. elongata, but sometimes it is divided 
into two by a band of collenchymatous cells at right angles 
to the substratum. The thallus grows rapidly in length, 
and occasionally branches exogenously, the branches lying 
parallel to the thallus from which they sprang. 
(48J 
