OF CEYLON AND INDIA. 
317 
which Warming showed to be endogenously formed. These 
soon begin to make their appearance. The first but not the 
only place in which they appear is commonly in the angles 
between the branches of the thalli, as shown in PL XI., fig 2. 
They appear in this position without any actual separation 
or splitting of the thallus taking place. They also very 
commonly spring from the thin marginal portions of the 
thallus or its branches. They appear at first as little swell- 
ings of the upper surface of the thallus, formed, as Warming 
has described, by an endogenous growth under about two 
layers of cells, and soon burst out through the upper epider- 
mis. The diagrammatic sections in PL XI., figs. 6, 7, show 
how the growing point is formed by transverse divisions of 
the parenchyma cells between two vascular bundles ; the 
appearance of the tissue under the rosette is not unlike that 
under the cups of an Æcidium. The growing apex itself 
does not come above the surface of the thallus, but the leaves 
burst through and spread themselves out in a symmetrical 
rosette. They are usually linear or lanceolate in form, and 
have the same structure as the leaves at the growing point 
of the thallus itself. Beyond what has been described, no 
order seems to be followed in the development of these 
secondary shoots upon the thallus, new ones often appearing 
ajnong the old. On the whole, however, they appear in 
longitudinal rows down the centre of the strips of thallus ; 
in the narrow forms only one or two rows may be found 
(XI., 9), in the more flabelliform several (XI,, 2). 
When these endogenous shoots appear upon the upper sur- 
face of the thallus, but not actually at the edge of it, they 
show radial symmetry, as just described, but when, as in 
rejuvenescence especially is not infrequently the case, they 
form upon the margin of the thallus, they show a distinct 
dorsiventrality from the very first. PL XI., fig. 8, shows such 
a shoot soon after its appearance. It rapidly develops into 
a growing point exactly like that at the tip of the main 
thallus, and may commence at once to form new branches of 
the thallus, or to form a flower, according to the time of year. 
