Growth Studies. 
II. An Interpretation of some Growth-curves. 
BY 
J. H. PRIESTLEY and W. H. PEARSALL. 
With four Figures in the Text. 
Introduction. 
HE first paper of this series contained the results of a quantitative 
JL study of the growth of roots from Tradescantia and tomato cuttings. 
Graphically expressed, these results give a series of S-shaped curves, the 
initiation of each curve coinciding with the development of a new crop of 
roots of a subordinate order of branching. 
Curves of this type are very familiar in quantitative investigations on 
growth, when the results are expressed simply as the record of mass, 
volume, area, or length after different periods of time. This type of curve 
may therefore be taken as characteristic of many growth reactions. It is 
proposed to consider a possible explanation of the S curve as exemplified 
in the growth of yeast and of roots. 
No attempt will be made to summarize the extensive literature dealing 
with the problems of growth. A full discussion of much of the earlier 
work is given by DArcy Thompson (19), and in this paper reference will 
be made only to facts of interest from the particular point of view here 
developed. It suffices to point out that the earlier attempts at the 
explanation of the growth-curve fall into two categories. They are either 
attempts to find a mathematical formula for the graphical results obtained 
(Robertson (11, 12, 13), Gregory (7), Schuepp (15, 16)), or else they try to 
find analogies in curves expressing the relation between other types of 
reaction and time. The latter method of attack has resulted in the 
consideration of the analogy between growth and an autocatalytic chemical 
reaction. 
Much profit can be derived from the consideration of the arguments 
advanced in these first attempts at generalization in a complex field, and as 
these aspects of the case have been too summarily dismissed by West, 
Briggs, and Kidd (20), in a recent survey of the literature, it may be useful 
to outline some of the more important points of interest. 
[Annals of Botany, Vol. XXXVI. No. CXLII. April, 1922.] 
