IV. Correlations in Development . 
269 
Table IV. 
Average Dry Weight Increase per Day of Pea Roots. 
Before secondary roots. After secondary roots. 
Stem in light 15 0 C. 
i-6 mg. 
2.1 mg. 
i -5 
i *5 
16 
2.2 
Stem in dark 15 0 C. 
2.4 
2.9 
1, 7 
1.9 
1.6 
i *5 
Average I5°C. 
i -7 
2-0 
Stem in dark 25 0 C. 
3-3 
6-1 
These results do not include periods when root growth was seriously 
decreased. They are obtained by finding the average growth rate from 
curves such as are given in this paper. For example, the figures at 25 0 C. 
are taken from Series III, the periods being ij to 4 days and 6 \ to 8J days. 
The growth curves are practically straight lines between the points taken. 
The only case in which a markedly increased average growth rate 
results after secondary root formation is at the higher temperature, and in 
this case we are probably justified in assuming that the rate of hydrolysis of 
food materials would be at least twice, probably about three times, as rapid, 
compared with that at a temperature of I5°C. Preliminary estimations 
of the temperature coefficient of protein hydrolysis in bean cotyledons seem 
to support this assumption. Thus it appears probable that at a temperature 
of 15 0 C. food supply is the factor limiting root growth after the develop¬ 
ment of lateral roots. Since the forms of the curves for stem growth 
approximate fairly closely to those for the normal autocatalytic reaction— 
which is now recognized as being a form of curve common in growth pro¬ 
cesses—it does not appear to be justifiable to assume any limitation of 
growth rate in the case of the stem, apart from that implied by a com¬ 
parison between growth and an autocatalytic reaction. Hence the food 
supply to the root must be regarded as the residue remaining after the stem 
has withdrawn its supply. 
The point of view developed above is in agreement with the earlier 
results of Kny ( 4 ) and Townsend (10). The papers of the former are 
somewhat unsatisfactory, but this author considered among other things the 
effect of removing the shoots from seedlings on the amount of root 
developed. This treatment, so far as any conclusion is possible from Kny’s 
results, generally causes increased root growth in both Zea Mays and Vicia 
Faba , though in the latter case this effect is delayed. Townsend ( 10 ) also 
gives data for the effect of shoot removal on the rate of root growth in the 
same two plants. The roots of seedlings thus treated were 26 to 33 per 
cent, longer than those of normal plants five days after treatment. His 
results seem to be beyond suspicion, and justify the view that removal of 
the shoot allows an increased rate of food delivery to the root meristem. It 
