236 Priestley and Ever shed. — Growth Studies. I. 
shoot, when the subsequent curve of growth may be expected to merge into 
that characteristic of the sum of the activities of the plant. 
Fig. 6. The data of Table I plotted as a rate-curve showing Sachs’s 1 Grand Period ’ 
of growth. The first part of the curve is suggested. 
6. Summary. 
1. The data obtained in some quantitative studies of root growth are 
presented in the form of tables and curves. 
2. Roots were chosen, in these experiments, to avoid the more direct 
influence of the progressive change in photosynthetic area during growth. 
3. Cuttings were used, instead of seedlings. In the case of Trades- 
cantia. the cuttings were of uniform weight. 
4. When plotted, the data provide examples of successive curves of the 
characteristic S type so frequently found in growth experiments. 
5. The time of transition from one S curve to the next is shown to 
coincide with the time of appearance of a crop of rootlets of subordinate 
branch order. 
6. It is pointed out that a single S curve corresponds to the Sachs 
‘ Grand Period ’ curve for root growth, and that if his method of measure- 
ment had permitted, the rate of growth of roots would have provided 
a series of such ‘ Grand Period ’ curves. 
References. 
1. Blackman, V. H. : The Compound Interest Law and Plant Growth. Ann. Bot., xxxiii. 
353-6 o, 1919- 
2. Brenchley, Winifred : On the Relations between Growth and the Environmental Conditions 
of Temperature and Bright Sunshine. Ann. of App. Biol., vi. 211-44, I 9 2 °* 
3. Briggs, G. E., Kidd, F., and West, C. : A Quantitative Analysis of Plant Growth. Ann. of 
App. Biol., vii. 103-23 and 202-23, 1920. 
