CH. Ill] THE KATE OF GROWTH 87 



the flattened, lancet-shaped Leptocephalus larva and the httle 

 black cylindrical, almost thread-like elver, whose magnitude is 

 less than that of the Leptocephalus in every dimension, even, at 

 first, in length (Fig. 15). 



From the higher study of the physiology of growth we learn 

 that such fluctuations as we have described are but special inter- 

 ruptions in a process which is never actually continuous, but is 

 perpetually interrupted in a rhythmic manner*. Hofmeister 

 shewed, for instance, that the growth of Spirogyra proceeds by 

 fits and starts, by periods of activity and rest, which alternate 

 with one another at intervals of so many minutes (Fig. 16). And 



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



minutes 



Fig. 16. Growth in length of Spirogyra. (From Ostwald, after Hofmeister.) 



Bose, by very refined methods of experiment, has shewn that 

 plant-growth really proceeds by tiny and perfectly rhythmical 

 pulsations recurring at regular intervals of a few seconds of time. 

 Fig. 17 shews, according to Bose's observationsf, the growth of 

 a crocus, under a very high magnification. The stalk grows by 

 little jerks, each with an ampHtude of about -002 mm., every 



* That the metamorphoses of an insect are but phases in a process of 

 growth, was firstly clearly recognised by Swammerdam, Bihlia Naturae, 1737, 

 pp. 6, 579 etc 



t From Bose, J. C, Plant Eesponse, London, 1906, p. 417. 



