AUTOCATALYTIC REACTION 179 



form of a curve (Fig. 10) their incidence is sufficiently close 

 to give support to the thesis, especially when allowance is 

 made for the experimental errors. 



To what extent and in what degree growth processes may be 

 correlated with this law is uncertain. The observations of 

 Gregory show that the curves of increase in the area of the 

 leaf surface of cucumber plants are of the S form and can be 

 represented by the formula of such a reaction. In the earlier 

 stages of growth this increase also is in accordance with the law 

 of compound interest. There is thus a choice between the 

 two expressions : the compound interest law is a conception 

 rather than a physiological constant, but even so Gregory 

 considers it to have the advantage over the law of autocata- 

 lytic reactions in that it is independent of hypothetical mech- 

 anisms of growth. For it is obvious that if growth is an 

 expression of the activity of some catalytic agent, that agent 

 must be sought out ; according to Robertson * the lipoids 

 may subserve the required function. 



Robertson's thesis, in essentials, is supported by the ob- 

 servations of many investigators : Rippel f finds it more 

 satisfactory than others, and has applied it to his and 

 Oskar's $ observations on the increase of growth in response 

 to nitrate manuring. Prescott § is satisfied that the flowering 

 curve of the cotton plant can be accurately expressed by an 

 equation which is essentially that of an autocatalytic chemical 

 reaction. Reed and Holland || found that the rate of growth 

 of the sunflower closely approximates the course of such a 

 reaction. Reed ^f also observed that the rate of increase 

 in the height of walnut and pear trees showed growth cycles 

 throughout the growing season ; in each cycle the growth 

 rate corresponded to an autocatalytic reaction. Similar re- 

 sults have been obtained by Gustafson ** for Cucurbita Pepo 



* Robertson : " Arch. Entwicklungsmech. Org.," 1913, 37, 497- 



f Rippel : " Ber. deut. bot. Ges.," 1919, 37» l6 9- 



1 Rippel and Oskar : " Biochem. Zeit.," 1925, 155, 133. 



§ Prescott : " Ann. Bot.," 1921, 36, 121. 



|| Reed and Holland : " Proc. Nat. Acad. Sci.," 1919. 5» *35- 



•{ Reed : '* Journ. Gen. Physiol.," 1920, 2, 545 ; " Amer. Naturalist," 



1924.58.337- 



** Gustafson : " Plant Physiol.," 1926, I, 265 ; see also id., 1927, 2, 153. 



12 * 



