Jackson. — Anatomical Structure of the Roots of Barley . 25 
Haberlandt, 1 where the endodermal cells opposite the protoxylem remain 
unthickened and serve as the connecting link between the central cylinder 
and the cortical parenchyma. 
Fully developed roots. Fig. 3 shows the appearance of a transverse 
section of an old root. The stele here consists of a strongly marked 
cylinder of much-thickened tissue, and the central duct is bounded by 
a thick wall and closely resembles a xylem vessel. Such an axile vessel 
occupying the centre of the root is described by Haberlandt 2 for the 
primary roots of Graminaceae and certain other Monocotyledons, and by 
Kroemer 3 for Zea Mais> but is not mentioned by Jeffrey, 4 who states that 
for the ‘ mass of monocotyledonous roots ’ the 4 central region of the root is 
occupied by a well-marked pith ’. 
The number of xylem groups 
seem to be typically from six to 
eight ; in the root shown in 
Fig. 3 there are seven groups 
each containing one large vessel, 
and alternating with seven groups 
of phloem, all the intervening 
tissues consisting of thickened 
cells. 
The endodermis is excep- 
tionally thick-walled, a con- 
dition which appears constantly 
throughout the old branched 
roots. This much-thickened en- 
dodermis is a characteristic of 
several monocotyledonous plants. 
It is illustrated for Allium by Haberlandt, 1 for Zea Mats by Kroemer, 3 for 
Oryza by Nageli and Leitgeb, 5 and for Dracaena by Lindinger. 6 Sections 
taken at different levels through a branched root 28 in. in length reveal the 
stages shown in Fig. 2 and 3. Immediately behind the root-tip the structure 
is like that of the young root in Fig. 2, while in the middle portion of the 
root and near the grain the thickened stele of Fig. 3 is found. 
A longitudinal section of an old root shows that the central duct is 
1 Haberlandt, G. : Physiological Plant Anatomy, p. 370. Trans, from 4th German ed. by 
Montagu Drummond, 1914. Macmillan & Co., Ltd., London. 
2 Loc. cit. 
Kroemer, Karl : Wurzelhaut, Hypodermis und Endodermis der Angiospermenwurzel. Biblio- 
theca Botanica, Stuttgart, 1903, Heft 59, pp. 151, 6 Taf. 
4 Jeffrey, Edward Charles : The Anatomy of Woody Plants, p. 158. Univ. of Chicago, 1917. 
Nageli, C., and Leitgeb, H. : Entstehung und Wachstum der Wurzeln. Beitrage zur wissen- 
schaftlichen Botanik, Heft iv, pp. 73-160. Taf. xi-xxi. 
6 Lindinger, L. : Monokotylenwurzel. Bot. Centralbl., Jena, Beiheft 19, Abt. 1, 1905, 
pp. 321-58. 
