J ackson. —Anatomical Structure of the Roots of Barley. 23 
hairs have not been rubbed away. This fact has been corroborated by 
examination of the washed roots under the binocular microscope, whereby 
the existence of abundant root-hairs from the tip of the 4 unbranched 5 roots 
right up to their point of origin is made perfectly clear, while in the 
branched roots hairs are found only for a short distance behind the root- 
tips of the main roots and their lateral branches. 
The general appearance of the root system of a plant bearing typical 
branched and ‘unbranched 5 roots is shown in Fig. 1. In this case there are 
two short 4 unbranched ’ roots, S 8 and S 9 , coming off from the grain, though 
they do not arise from quite the same point as the typical branched roots, 
Rj— R 8j of the primary root system. The majority of the 4 unbranched ’ 
roots, Sj-Sp spring from a node half an inch above the grain. These roots 
exhibit various stages of development, from the totally unbranched type S x 
to the type S 7 which is still markedly thicker than any of the roots of the 
primary system, but also bear a good number of laterals. Careful study of 
the literature on roots has failed to reveal any work on the anatomy or on 
the functions of these ‘ unbranched 5 roots, although the phenomena of 4 white 
roots’ is thoroughly well known to the farmer. There is undoubtedly 
a connexion between the tillering of a plant and its formation of 4 unbranched ’ 
roots. From a series of pot cultures in which barley was grown, two plants 
were washed out each week and their root systems examined. Tillering 
was observed in all the plants just after the first 4 unbranched ’ roots had 
appeared. This is also found to be the case in winter-sown wheat and oats 
growing in the field. During the winter the plants are growing very little, 
but in the spring they begin to push forward, and if a plant just starting to 
tiller is examined it is found that white 4 unbranched ’ roots are practically 
always present. These roots appear also in the field barley, but this being 
a spring-sown crop the 4 unbranched ’ roots appear at a much earlier stage 
in the plant’s history than in either wheat or oats. That farmers recognize 
the existence and importance of these 4 unbranched ’ roots is clear from the 
general practice of horse-hoeing a wheat crop until the 4 change of root ’, 
which is really the formation of the white roots . 1 After this has happened 
it is considered dangerous to horse-hoe, as it would probably involve injury 
to the newly-formed roots, most of which it must be remembered are nearer 
the surface of the soil than are the primary roots, since they spring from the 
node above the grain. 
The present paper embodies the results obtained from an anatomical 
investigation of the two types of roots as found in barley plants grown in 
soil and in water cultures. 
1 The term * change of root ’ seems to be of general occurrence among farmers, but no reference 
to it has been traced in any of the books on agricultural practice. 
D % 
