Ill] 



OF PERIODIC GROWTH 



171 



A crocus grows, he says, by little jerks, each with an amphtude of 

 about 0-002 mm., every twenty seconds or so, each increment being 

 followed by a partial recoil* (Fig. 40). If this be so we have come 



20 40 60 80 100 120 140 160 180 200 220 240 260 



minutes 



Fig. 39. Growth in length (mm.) of Spirogyra. From Ostwald, after Hofmeister. 



Fig. 40. 



seconds. 



Pulsations of growth in Crocus, in micro-millimeter? 

 After Bose. 



down, so to speak, from a principle of continuity to a principle of dis- 

 continuity, and are face to face with what we might call, by rough 

 analogy, "quanta of growth." We seem to be in touch with things 

 of another order than the subject of this bookt. 



* J. C. Bose, Plant Response, 1906, p. 417; Growth and Tropic Movements of 

 Plants, 1929. 



t There is an apparent and perhaps a real analogy between these periodic 

 phenomena of growth and the well-known phenomenon of periodic, or oscillatory, 

 chemical change, as described by W. Ostwald and others; cf. (e.g.) Zeitschr. f. 

 phys. Chem. xxxv, pp. 33, 204, 1900. 



