Roots of some North African Desert-Grasses. 329 
Habit and Habitat. 
Aristida pungens is very widespread in the North African Sandy 
Deserts. In the Algerian Sahara it is characteristic of, and appears 
to be confined to, the sandy as opposed to the stony desert. In this 
region the grass is called the “ Drin.” Massart 1 states that in 
appearance it somewhat resembles the Ammophila arenaria of 
European dunes and that it is important as a grazing grass in the 
desert. The peculiar habit has been fairly fully described by 
Volkens 2 and also by Massart, 3 The roots spread out to a great 
distance from the stock of the grass, 20 metres being probably far 
too low an estimate, and maintain a position a few inches below, 
and more or less following the undulations of the surface of the 
sand. The roots are thin and cord-like, maintaining a fairly uniform 
thickness throughout, and surround themselves with a peculiar 
sheath, composed of agglutinated particles of sand—“ wie das Bein 
in der Hose, oder besser und asthetischer ausgedriickt, wie eine 
Phryganeenlarve in dem selbst gebauten Gehause.” 4 This sandy 
sheath is fairly hard and resistent, retaining its shape when the root 
dries up, though it then becomes very brittle : this feature is clearly 
shown in dried herbarium material. The root-hairs, generally the 
most ephemeral perhaps of all the organs of a vascular plant, 5 in 
this species and in a few similar Monocotyledons, do not disappear, 
but, according to Volkens and Massart, remain throughout the 
length of the root. 
As was to be expected from this characteristic habit the mor¬ 
phology and anatomy of the roots, exhibit features which are 
interesting in relation to biological adaptation. 
The material upon which the present work was carried out was 
collected by Mr. A. G. Tansley at Ain Sefra in the Algerian desert 
while on an expedition during the spring of 1910. The grass grows 
in abundance on the great sand dunes of Ain Sefra, 6 but consi¬ 
derable difficulty was experienced in obtaining root-tips owing to 
the great length of the roots, which were very easily broken in the 
attempt to follow them to their extremities. The material, which 
1 Massart, Jean. Un Voyage Botanique au Sahara. Bull. Soc. 
Roy. Bot. Belgique, Tome XXXVII., 1898. Especially pp. 
237-240. 
2 Volkens. Flora der .Egyptisch-Arabischen Wiiste. Berlin, 
1887, pp. 25, 26, etc. 
8 Massart, l.c. 
4 Volkens, l.c., p. 26. 
‘ Massart, l.c., p. 238. 
0 v. Karsten & Schenck. Vegetationsbilder, 6 Reihe, Heft 
Taf. 24, Jena, 1908. 
