30 



same amount of nitrate, owin^ to the accumulation of the products 

 of assimilation. 



in. Winifred E. Brknchley and Violet G. Jackson. 

 " Root Development in Barley and Wheat under 

 different conditions of Growth." Annals of Botanv, 

 1921. 



InA^estigations have been begun on the effect of various 

 manures as superphosphate, sulphate of potash and nitrate of 

 soda on the root systems of barley and wheat. Most of the ex- 

 periments were made in pot cultures and the roots washed out at 

 regular intervals to obtain the various stages of development. 

 Two forms of roots are produced : — 



1. — Much branched roots, most of which proceed from the 

 grain. These are rather thin, long, and bear very numerous fine 

 laterals, with root hairs only near the tip. 



2. — Thick unbranched roots arising from tlic nodes as well as 

 the grain, white in colour, and densely clothed with root hairs 

 throughout their length. At a later stage these roots branch and 

 approximate more closely to the others in appearance. 



With barley, superphosphate encourages the development of 

 unbranched roots, sodium nitrate having no effect. When the 

 plants are about three months old no more unbranched roots seem 

 to be formed. The maximum root development was reached at 

 about the time that the ears were ready to emerge from their 

 sheaths, i.e., v/hen pollination and fertilisation of the ovule were 

 about to take place. With superphosphate alone and with nitrate 

 alone, however, this maximum was reached somewhat earlier, s(^ 

 that apparently root growth culminated with the final stage of pre- 

 paration by the plant for grain formation. In other words, during 

 the period of purely vegetative growth the plant needs targe sup- 

 plies of nitrogen and ash constituents to aid in building up a strong 

 shoot in readiness for grain formation, and the root steadily in- 

 creases m order to be able adequately to cope with this demand. 

 During the reproductive phase, on the other hand, vegetative 

 development is reduced to a minimum, and the whole of the plant's 

 energy is diverted towards the grain. Although nitrogen and ash 

 constituents are just as essential as before, the area of supply is 

 increased, as migration of these substances from the straw into the 

 grain goes on from the outset. This reduces the strain on the 

 root, and as such a large absorbing area is no longer required it 

 appears tJiat the excess provision may be got rid of by a steady 

 process of deca}-, as the weight of the root steadily decreases when 

 once the maximum is reached. The ratios of root to shoot cd 

 different periods are also discussed, a great increase of the 

 shoot/ root ratio occurring where the unbranched roots cease to he 

 formed. 



With wheat the unliranched roots increase in numbers less 

 rapidly than in bark'y, but persist as such for a longer period. 



There is in wheat nothing to correspond with the sudden dis- 

 appearance of white roots which occurs in barley about 11 weeks 

 after sowing, for in wheat the decline in white roots coincides with 

 the decrease in weight of the complete root system, whereas in 

 barley the formation stops suddenly when the ratio between shoot 

 and root growth begins to change. 



