Jackson. — Anatomical Structure of the Roots of Barley. 27 
thin-walled cells with square ends, and these are separated from the 
piliferous layer by the parenchymatous cells of the cortex. The xylem 
and phloem lie along different radii, therefore a longitudinal section passing 
through the xylem does not pass through the phloem, so that phloem tissue 
does not appear in this section. 
These primary roots emerge from the grain, and soon reach a length 
of about 5 in., when they begin to branch freely. The origin of these 
lateral branches is in some sections shown to be a group of meristematic 
cells abutting on the endodermis. These cells are full of cell contents and 
take up any stain very readily. In this condition they resemble the 
formation of lateral roots in Oryza , as described by Nageli and Leitgeb. 1 
The meristematic stage is, however, soon over ; the lateral root grows out, 
and most frequently adjacent sections through the point of emergence 
present the appearance shown in Figs. 4 and 5. 
Branched roots are found coming from the node as well as from the 
grain. Those from the grain are present in the embryo itself and form 
the primary root system, but those from the node are adventitious in origin. 
The structure, however, is the same, both for the primary and for the 
adventitious roots, and in each case transverse sections show the typical 
thick-walled endodermis and single large axile duct surrounded by much- 
thickened tissue. 
Anatomy of 4 Unbranched ’ Roots. 
Young root . The structure of the ‘ unbranched ’ roots differs con- 
siderably from that of the branched type. The appearance of a section 
of a typical young 6 unbranched ’ root is illustrated in Fig. 6. At this stage 
the whole of the stelar tissue is thin-walled ; the central region consists of 
a core of parenchymatous cells traversed by several large ducts arranged 
in a circle. In this case six ducts are present, but the number varies for 
different roots. The xylem and phloem are not yet differentiated, so that 
outside the circle of ducts lie three or four rows of parenchymatous cells 
similar to those of the central core. These are bounded by the pericycle, 
which is distinguishable by its radially elongated cells. The cells of the 
endodermis are elongated tangentially, and are thus distinguished from the 
pericycle on the inside and from the cortex on the outside. Eight or nine 
rows of parenchymatous cells form the cortex, and these are bounded by the 
thin-walled cells of the piliferous layer. 
Intermediate stage between a young and an old root. The structure of 
a slightly older root is shown in Fig. 7, which illustrates a section taken at 
a point about half an inch behind the tip of an ‘ unbranched ’ root three 
1 Nageli and Leitgeb : loc. cit. 
