Wheat tinder Different Conditions of Growth. 541 
It may be suggested that part of the loss may have been due to the 
roots becoming more and more brittle and breaking off at the ends in the 
process of washing. If, however, this had been the case to any marked 
degree traces of the broken roots would have been observed during 
washing, as this was conducted with the utmost care and watchfulness. 
Corroboration may be obtained from two sources. 
(a) When barley plants are observed in the field the root system at 
harvest time seems small in comparison with what it is at earlier stages of 
growth. 
(b) In water cultures in which peas were grown, dried and weighed at 
regular intervals during growth, a definite fall in the weight of the root set 
in some time before the plants had completed their growth. The fall in 
this case must necessarily have been real, and due to decay of plant tissues, 
as under the particular experimental conditions it was possible to recover 
the whole of the root without danger of loss. 
In some cases it appeared that the maximum root development was 
reached at about the time that the ears were ready to emerge from their 
sheaths, i. e. at the time that pollination and fertilization of the ovule were 
about to take place. With superphosphate alone and with nitrate alone, 
however, this maximum was reached somewhat earlier, so that apparently 
root growth culminated with the final stage of preparation by the plant for 
grain formation. In other words, during the period of purely vegetative 
growth the plant needs large supplies of nitrogen and ash constituents to 
aid in building up a strong shoot in readiness for grain formation, and the 
root steadily increases in 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 
now 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 . 1 
This reduces the strain on the root, and as such a large absorbing area is 
no longer required it appears that the excess provision may be got rid 
of by a steady process of decay. Analyses indicate that by the time 
desiccation of the grain sets in, about three weeks before harvest, the whole 
of the nitrogen and ash required is already in the plant, so that the 
work of the root, other than as a water-absorbing organ, is practically 
complete. 
weeks earlier showed a similar decrease in weight to all the other types, and if this decrease had 
continued its normal course to the end the superphosphate and nitrate plants would have fallen into 
line with all the others. 
1 Brenchley, W. E. (1912) : The Development of the Grain of Barley. Ann. Bot., xxvi, 
pp. 914-19. 
