3 2 Jackson. — Anatomical Structure of the Roots of Barley. 
piliferous layer 
cortex. 
were found in which a section near the grain shows five large ducts 
traversing a stele in which all the tissues are thickened, while near the root- 
tip only one central space occurs in a stele of the type found in the young 
branched roots. 
The outstanding differences between the typical ‘ unbranched ’ roots 
and the roots which were originally * unbranched * but have assumed 
a branched habit is that in the former the young root shows the charac- 
teristic unthickened stele with its central region traversed by four to six ducts, 
while the latter possesses a stele with a considerable quantity of sclerized 
tissue and only one, or at the 
most two, central ducts. The 
older parts of the root resemble 
each other in general structure, 
but the stele of the ‘ unbranched ’ 
root shows less thickening than 
that of the transition root. 
Comparison of the anatomy 
of the branched and the ‘ un- 
branched' roots. A certain num- 
ber of measurements were made 
of the sections of the two types 
of roots obtained from five sets 
of differently manured pot cul- 
tures. The material available 
was limited, but, with the excep- 
tion of the superphosphate and 
potash manuring, measurements 
were obtained of two branched 
and two ‘ unbranched ’ roots from 
all the manurial types. Two 
diameters at right angles to each 
other were measured for the 
whole root, the stele, and for the central duct or ducts. It must be remem- 
bered that, when this material was being preserved, it was not realized that 
the ‘ unbranched ’ roots ultimately resembled the branched type, so that in 
certain cases roots which were originally of the ‘ unbranched ’ type were 
preserved as typical branched roots. The measurements of these transition 
roots together with those of their corresponding true ‘ unbranched ’ roots 
are collected together in Table II, while in Table I are the measurements 
of the true branched and ‘ unbranched ’ types. It will be noticed that in 
both cases where originally ‘ unbranched * roots were taken as branched 
roots, the plants had been treated with superphosphate, and this is a manure 
which tends to hasten the formation of ‘ unbranched 5 roots, so that at 
5 a rle' 
part of a T.J: of a 
“ Transition " Root. 
(taken near roat-t/pj(r«6\ 
passage cells. 
xy/em vessel, 
protoxylem. 
Fig. ii. 
