556 Brenchley and Jackson. — Root Development of Barley , &c. 
tend to have a shorter growing season than deep-rooted crops like 
wheat. 
2. Influence of different types of manuring on root growth. The effect 
of manuring on root growth in pot culture has been considered in the earlier 
part of the paper, but may be summarized briefly here. 
In barley the use of artificial fertilizers, whether containing K, N, 
or P, induce a great increase in root development, this being most marked 
in the presence of sodium nitrate, either alone or in conjunction with 
superphosphate. With zvheat , on the contrary, nitrogen manuring failed to 
bring about any increase, while the improvement with superphosphate and 
superphosphate + potash was far less evident than in barley. 
In barley, again, the number of ‘white roots’ was distinctly increased 
by the use of superphosphate, but with wheat the ultimate number of these 
roots was much the same whatever the system of manuring. It is not 
possible to say definitely whether these results would hold good under 
normal conditions of cultivation, as the soil conditions presented in pot 
cultures are so peculiarly favourable that it would be unfair to draw from 
them any conclusions with regard to similar experiments in the field. 
Apart from the question of depth of rooting the formation and function 
of the ‘ white roots ’ offer a promising field for inquiry. A comparison of 
the anatomical structure of the ordinary and white roots is being made by 
one of us, and discussion of the subject will therefore be postponed till 
a later paper, when more information will be available. 
