Roots of some North African Desert-Grasses. 331 
Grttn to remove some of the stain from the cell-contents. Gentian 
Violet, Orange G combinations and Delafield’s Haematoxylin were 
also useful. 
External Morphology. 
The roots as already mentioned are long and have an average 
thickness of about £ inch or 6 mm. To judge from the herbarium 
material branching is very rare, each root being one long cord-like 
organ. They taper rapidly towards the tip and here there is little 
sand adhering. The stele forms a small wiry strand, sharply 
marked off from the wide cortex; the latter can be easily pulled 
away leaving the stelar strand quite clean. Outside the cortex is 
the “ caddis-worm ” case, as it may be fancifully called, and when 
this has been removed the root-hairs can be seen on the older 
portions of the root. Hairs seemed to be always present on the 
older parts of the spirit material, except at one branching knot, 
evidently of an old root, where hairs were quite absent. Herbarium 
material examined with a simple lens, shows the hairs persisting 
right up to the point of origin from the stock. They project only a 
short distance from the sandy sheath, and probably when this is 
quite complete they do not emerge from its outer surface. 
In dried material, the cortical zone has generally collapsed 
and almost disappeared, leaving the central stelar strand surrounded 
loosely by the sandy sheath. 
Anatomy. 
In dealing with the anatomy the various tissues are traced 
backwards from the root-tip to the adult structure. 
In general the relation of the meristematic layers to the root- 
cap is of the so-called “ liorhizic type” of Van Tieghem 1 which is 
characteristic of Monocotyledons. Here the root-cap is quite dis¬ 
tinct from the outer layers of the cortex, and is formed by special 
meristematic cells, lying just outside those which give rise to the 
piliferous layer of the root. 2 The tissues of the central cylinder on 
the one hand and of the piliferous layer on the other, apparently arise 
from separated meristems, much as in the usual Graminaceous type 3 
so that it is needless to describe their origin in further detail. 
The root-cap is composed of large cells towards the exterior and 
smaller regularly arranged ones within. The outer cells are 
1 Van Tieghem. Traite de Botanique, 2nd edition, Partie I., pp. 
696 et seq, Paris, 1891. 
2 Van Tieghem, l.c., p. 698, and also Bonnier and du Sablon, Cours 
de Botanique, Paris, 1901, Vol. I., p. 341 et seq. 
3 Flahault. Ann. Sci. Nat. Bot., Ser. 6, tome 6, pp. 20 and 28, 
1878, 
