Roots of some North African Desert-Grasses. 333 
contents, and by the presence of a large conspicuous nucleus in each. 
The nuclei, whose fixation was very indifferent, are situated rather 
towards the bases than the apices of the cells (Figs. 2, 3 and 4). 
The regularly arranged gland-cells are present for a distance of 
about J-inch (6 mm.), or a little more, behind the meristematic apex, 
and then seem to pass over gradually into cells of ordinary 
parenchymatous type, elongated in a tangential direction (Fig. 5). 
Text-fig. 1. Text fig. 2. 
Text-fig. 1. Photograph of part of transverse section of the root of 
Aristida pungens, showing the regular cortex with large lacunae, the exodermis 
(ex.), the endodermis (cn.), the wide sclerenchymatous pericycle (pc.) with 
numerous phloem groups iph.) situated in the bays, the alternating protoxylems 
(px.) opposite the projections of the pericycle. X 60diam. (app.) 
Text-fig. 2. Portion of transverse section of a root of Aristida pungens, 
nearly mature, showing the cells of the piliferous layer which have grown out 
to form short root-hairs. Root treated with hydrofluoric acid. x 102 diam. 
Beneath the secretory layer is a zone of thin-walled cells (about 
two cells thick) with less dense contents, seen especially well in 
transverse section just behind the root-cap. This probably corres¬ 
ponds to the “ exodermis ” or cuticularised hypodermal layer, as 
for example in Lygeum Spartum Lof. mentioned below. Within this 
exodermis is a region of several layers of closely packed cells, and 
