Jackson. — Anatomical Structure of the Roots of Barley. 39 
and the middle of the root consists of thin-walled pith cells traversed by 
four to six ducts. 
3. The chief function of the ‘ unbranched ’ roots is probably to pro- 
vide the plant with a plentiful supply of water and its dissolved food, at 
the time when vigorous growth is setting in. This function is provided 
for by : 
(a) abundant root-hairs ; 
(b) an increased number of large vessels and central ducts ; 
(c) the existence of a stele composed almost entirely of thin-walled 
elements. 
In conclusion I wish to express my thanks to Dr. W. E. Brenchley for 
her very helpful and ever-ready advice throughout the whole of this work. 
