Anatomical Structure of the Roots of Barley. 
BY 
VIOLET G. JACKSON, M.Sc. 
(. Rothamsted Experimental Station.) 
With twelve Figures in the Text. 
A BARLEY plant, if carefully removed from the soil when about 
six to eight weeks old, generally shows two distinct types of roots. 
The bulk of the underground system consists of long roots which branch 
throughout almost their entire length, but there are in addition a certain 
number of ‘ unbranched ’ roots. Most of these spring from one of the 
nodes above the grain and are therefore of later origin than the branched 
roots, which spring from the grain itself. They are of a very waxen white 
appearance and attain a length of several inches without giving off any 
laterals, but ultimately they branch and seem to approximate to the general 
root system. 
The occurrence and behaviour of these white ‘ unbranched * roots were 
studied at Rothamsted in the summer of 1920, and material obtained then 
was preserved with a view to ascertaining whether there existed any difference 
between the anatomical structure of the branched and the unbranched type 
of root. Material was also, obtained from a series of experiments in which 
barley was grown in water cultures. Very distinct white ‘ unbranched * 
roots are found in water cultures when the plants are removed from their 
solutions at the conclusion of the experiment, somewhat before maturity is 
reached. In addition to their white colour, ‘ unbranched ’ roots can be 
distinguished from branched roots by their greater thickness and by a much 
larger number of root-hairs. These latter are particularly noticeable in 
water cultures, where there is considerably less abrasion than occurs in 
the soil, but even in soil, if the plants are washed out as described in 
a previous paper, 1 it is always difficult to free the white 4 unbranched ’ roots 
from the tiny soil particles which adhere very closely along the whole length 
of the root. In a branched root, this closely adhering soil is only found 
in the region immediately behind the root-tip, presumably where the root- 
1 Brenchley, W. E., and Jackson, V. G. : Root Development in Barley and Wheat under 
Different Conditions of Growth. Ann. Bot., vol. xxxv, pp. 533-556, 1921. 
[Annals of Botany, Vol. XXXVI. No. CXLI. January, 1922.] 
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