285 
Festuca rubra near Cardiff. 
system of the axis divides into two distinct groups of bundles ; the 
larger group remains in the axis whilst the smaller group belongs 
to the primary branch. This latter, slightly higher up, resolves 
itself into six distinct bundles which appear as two groups of three, 
one group of which consists of larger bundles and passes up the 
primary branch axis, the other group of smaller bundles belonging 
to the secondary branch. Thus the vascular system of the secondary 
branch joins up with that of the primary forming a single group 
which takes its place in the main axis. 
V. —Temporary Modifications 
The effect of certain types of habitat is seen in modifications 
of external form and internal structure which are of a temporary 
nature, and there is a reversion to normal when the plant is 
transferred to normal conditions. 
Specimens of tenuifolia collected from scanty soil on exposed 
rocks have proved difficult to identify until transferred to the 
garden and their subsequent growth observed; They show a 
peculiar stunted growth, a kind of nanism, induced by the extreme 
xerophytic conditions under which they grow (Fig. 14). The leaves 
are shorter and more fleshy ; the laminae stand out from the axis 
and gently curve upwards. The base of the shoot is stouter and 
the plant more densely caespitose. The panicle is reduced to a few 
small spikelets. These modifications are the result of a very 
exposed situation, extreme dryness of habitat, and probably also 
halophytic influence. Similar modifications, though not quite so 
marked, are seen in the plants which grow on the scantier soil of 
the pebble-ridges, where great extremes of moisture and temperature 
on and near the surface must be encountered. 
VI. Summary. 
The three forms studied, which have been referred to the 
subvarieties grandiHora, tenuifolia and glaucescens respectively, are 
quite stable, distinct in both vegetative and floral characters, and 
in choice of habitat. 
The first form corresponds with Festuca rubra , var. 1 genuina> 
subvar /3. grandiflora (Hack). Its general habitat is a more or less 
mesophytic one and its morphological and anatomical characters 
are practically those of a mesophyte, though with certain xerophytic 
tendencies. It possesses fairly long, creeping rhizomes and is loosely 
sub-caespitose; well fitted for producing a rich carpet of vegetation. 
It has a well developed root-system and its dark green leaves 
are perfectly glabrous. Its panicle is loose and well-developed, 
and the spikelets are large. 
