OF CEYLON AND INDIA. 
367 
disc, but when the apical growth is rapid, it is lobed oi 
branched. When the disc form grows old, it is usually 
stout, and with the margins slightly turned up. The 
upward curve seems to be brought about as in Dicræa 
stylosa fucoides by greater meristematic activity and growth 
near to the edges. 
Accentuation of the growth of the sides of the base of the 
thallus results in a form like a bowl or cup, lobed or not, 
according to the relative rate of growth of the apices. When 
once the corner is turned, so to speak, the thallus continues 
to grow away from the rock in an ascending direction, and 
so the cup may reach a considerable size, as in several of 
the examples figured in PI. XXVI. 
The simplicity of the cup form may be complicated by 
further irregularity of growth in length and thickness at 
different parts, resulting in the very involved forms seen 
on the right in PI. XXVI. In all but the last two of these 
the foot or disc from which the plant starts may be seen. 
If the development of the thalli be very uniform, and the 
growing points do not outrun the tissue between, the cup or 
bowl may be very symmetrical, as in XXVI., 1 and 4. 
Sometimes one side grows faster than the other (this is the 
case especially when the plant is on a sloping rock, the lower 
side growing the faster), and a scuttle-shaped thallus is 
formed like that in PI. XXVI., fig. 3. 
Not infrequently the foot grows vertically by division 
and elongation of its cells, and thus forms a shorter or 
longer solid stalk (narrower than the actual foot, which 
usually forms a disc like that of Tristicha ramosissima), 
carrying up the disc or bowl upon its summit, as in 
PI. XXVI., figs. 1, 2, 3, 10. The first-mentioned figure re- 
presents a most symmetrical stalked cup, like the basal cup 
of the alga Himanthalia lorea. It is particularly interesting 
to see in these plants how many of the forms of the algæ 
of moving water they reproduce. 
The remarkable polymorphism of the thalli in this plant 
is thus very simply explained anatomically, and forms an 
