277 
Festuca rubra near Cardiff. 
arms are more nearly equal and have acute apices (Pig. 7 b). 
The lower portion is much more swollen in grandiflora than in 
either of the other two forms. The result is that the flowers of 
grandiflora open widely, whilst those of the other two open just 
sufficiently to allow the projection of stamens, between the two 
points of the paleae, and later the stigmas, between the two over¬ 
lapping edges of the paleae. At this stage the larvae of Thrips 
attack the flowers of grandiflora and the young ovules shrivel. 1 On 
the other hand the flowers of tenuifolia , even though growing side 
by side, are immune. Possibly Thrips has easy access to the 
ovules of grandiflora through the well separated glumes, whilst the 
closed glumes of tenuifolia make access difficult or impossible. 
Massee (10) has “ frequently seen the ear (of barley) well out of the 
leaf sheath, and many or all of the grains presenting a shrivelled 
appearance . . . due to the work of Thrips ceralium Halid.” 
The anthers dehisce about the second week in June. The 
almost sessile feathery stigmas are receptive about a week later. 
In subvar. tenuifolia the ovary after fertilisation elongates consider¬ 
ably and when full grown is about three mm. long. It has a deep 
median posterior furrow. It is ready for dispersal about the end 
of August. 
IV. —Comparative Anatomy and Histology. 
1. The Rhizome (Stoloii). 
Extravaginal branches of grandiflora and tenuifolia were 
sectioned across their basal internodes (Fig. 8). In grandiflora 
the epidermis is slightly cuticularised, but in tenuifolia the walls are 
thickened, with a well developed cuticle. The cells of the 
hypodermis in the latter are also somewhat thick-walled. In 
grandiflora there are only three to four layers of cortex, and when 
mature the cells below the hypoderm break down in places, 
forming large cavities; in tenuifolia there are about six layers of 
cortical cells which persist. The mechanical tissue is in the form 
of a tube which is more centrally placed in tenuifolia than in 
grandiflora. The radial and inner walls of the external fibres are 
much more thickened than the outer walls ; those placed between 
and within the vascular bundles are uniformly thickened (Fig. 8 c). 
In grandiflora there are about twenty-five vascular bundles ; in 
tenuifolia only about ten. They vary in size individually, but on 
the whole those of grandiflora are larger. They are of the usual 
grass type (Fig. 8 a and 8 b). 
1 Whether grandiflora would set good seed if protected from Thrips 
remains to be determined. 
