Roots on some North African Desert-Grasses. 337 
pericycle consisting of several layers of cells is present, though its 
cells are not so strongly thickened as in A. pnngens. The external 
elements of the protoxylems extend to within one cell of the 
endodermis while the phloem groups are placed in juxtaposition 
with the “capes” of the pericycle. Thus the arrangement of 
protoxylems and phloems is rather different from that obtaining in 
A. pnngens. There are also some small groups of phloem embedded 
in the sclerised conjunctive between the larger vessels of the meta- 
xylem. The pith is less thick-walled than in A. pnngens. 
LYCEUM SPARTUM Lofl. 
This species—the well-known “ Esparto Grass ”—grows in the 
Mediterranean region of Spain, Algeria, &cd A specimen gathered 
in the Algerian desert was growing on sand, apparently a common 
habitat of the species. 2 
A distinct sandy sheath was present on the roots in this 
material, but was not quite so thick or coherent as in A. pnngens. 
The root-hairs are short and hardly project at all from the sheath, 
even in the dried material. They are persistent to within an inch 
or so of the point of insertion of the root. 
The dried material was soaked out in alcohol for some time 
and then treated with hydrofluoric acid. Microscopic examination 
before treatment with acid showed the grains adhering closely to 
the outer surface as in A. pnngens. 
After the sand had been removed, sections exhibited a well 
preserved structure. The piliferous layer is normal in appearance 
and within it is a cortical zone composed of four or five layers of 
cells with very thick walls strongly cuticularised (Fig. 7). In the 
material thus treated it was not possible to make out any pits or 
passage cells, but such must exist if the root-hairs are functioning 
in this region—the latter presumption seeming very probable. 
On the whole the rough examination possible seems to point 
to an adaptation very similar to that in A. pnngens or A. obtnsa, 
but certainly not so well marked as in A. pnngens, together with a 
highly developed protective mechanism, in addition to that presented 
by the sandy mucilaginous sheath, and absent or much less developed 
in the species of Aristida. 
BROMUS TECT0RUM L. 
This species is widespread in Europe and in North Africa, 
growing on walls, arid places and in the desert. 3 
1 Boissier, l.c., p. 452. 
2 Warming, “The (Ecology of Plants,” p. 284, Oxford, 1909. 
s Boissier, l.c., p. 647. 
