Wheat under Different Conditions of Growth 555 
aeration than shallow-rooted. The latter tend to branch most freely near 
the surface of the ground, where aeration is good and soil temperature is 
favourable, the deeper rooted plants being less sharply limited in growth 
by the soil conditions. These conclusions were fully borne out by the 
Rothamsted results. Barley, typically shallow-rooted, responded at once 
to the favourable conditions of penetrability and aeration under pot-culture 
conditions, and developed a root system which corresponded closely with 
that of the typically deep-rooting wheat. In the field, on the contrary, 
where the soil was badly aerated and difficult to penetrate, the barley roots 
were short and very poorly developed, whereas those of the wheat were 
apparently able to strike more deeply and develop more strongly. 
Water and the available food-supply have considerable influence on 
development. Von Seelhorst working with rye, 1 wheat, barley, &c., found 
that when liberally fertilized the plants have a larger root system, the roots 
descending deeper into the soil and thus being able to withstand drought 
better. 
Cannon 2 states that soil temperature is another vital factor in 
determining the type of root growth, as roots which occupy different soil 
horizons in the same habitat are exposed to widely different temperatures 
at all seasons. In working with desert plants he found that the growth- 
rate of roots varies with temperature, that of deep-rooted plants being more 
rapid at all temperatures than that of shallow-rooted. No temperature 
readings were taken during the Rothamsted experiments, but it may safely 
be assumed that as the pots were relatively small and exposed on all sides 
to the air, the temperature of the soil at the bottom of a pot approximated 
more closely to that at the top than the temperature 14 in. deep in the 
soil to that of the surface soil. This being the case the temperature 
conditions were more favourable to the growth of roots in the pots than in 
the field, and this, added to the other favouring conditions of aeration and 
penetrability, probably helped the shallow-rooting barley to strike deeply 
and develop a strongly branched root system. 
Modestov 3 carried out experiments on the root development of races of 
the same species, and found that different races of wheat and oats grown 
under similar conditions showed essential differences in the length and 
weight of their roots. In oats the length of the roots was in inverse 
proportion to the time of ripening, deeper rooting resulting in later 
ripening. The idea suggests itself that possibly this may hold good 
outside the limits of a single species, as shallow-rooted crops like barley 
1 Seelhorst, C. von (1902): Beobachtungen liber die Zahl nnd den Tiefgang der Wurze'ln 
verschiedener Pflanzen bei verschiedener Diingung des Rodens. Jour. Landw., 1, No. i, pp. 91-104. 
2 Cannon, W. A. (1915) : loc. cit. 
3 Modestov, A. P. : Les racines des plantes herbacees. Kornevaia sistema Travianist’kh. 
Rastenii., Moscow, I. N. Kushnerev, 1915, No. 1, pp. 223. See Exp. Stat. Rec., vol. xxxvi, 1917, 
p. 223. 
