Festuca rubra near Cardiff. 279 
3. The Adventitious Root. 
In grandiflora two or three adventitious roots arise simul¬ 
taneously with the axillary branch and below it; in tenuifolia there 
is usually only one root, which is almost exactly below the midrib 
of the subtending leaf. This may be supplemented by others, 
according to the nature of the soil. As the young root grows out 
through the cortex the cells of the latter form a sheath of two to three 
layers which grows out with it, acting like the coleorhiza to the 
radicle The first roots are all tetrarch, their finer branches diarch. 
Fig. 9. Trausverse section of fine root of (a) grandiflora, (b) tenuifolia. x 330. 
Transverse sections show the root of both subvarieties to have 
much the same general structure. The piliferous layer of 
grandiflora (Fig. 9 ?) has few root hairs, a cortex of two layers of 
parenchyma, an endodermis with “ horseshoe ” thickening broken by 
two sets of passage cells, a pericycle of one layer of regular cells 
alternating with those of the endodermis, and a diarch xylem 
plate. In tenuifolia (Pig. 9 b) the root is similar, but has less than 
half the diameter; the root hairs are quite as stout and relatively 
more numerous. In later formed roots of both forms, when the root- 
hairs have ceased to function, the piliferous layer collapses, the 
exodermis becomes suberised and the endodermis uniformly 
thickened; the xylem is tetrarch to polyarch. The whole of the 
cortex may later wither, but it persists around the endodermis and 
in tenuifolia the cell-walls of the pericycle become thickened so 
that it forms a second protective layer within the endodermis. 
