No. 502] CHEMICAL MECHANICS IN LIVING PLANT 651 



lines, with the different food materials as limiting factors, 

 should give instructive results. 



We turn now to consider the growth of a flowering 

 plant. Here conditions are more complex, and we know 

 that at the flowering stage or end of the season the 

 growth diminishes considerably. This difference from 

 a simple alga or bacterium we can only regard as a sec- 

 ondary acquisition in relation to the external conditions— 

 either a reaction to a present external stimulus or to the 

 memory of past stimuli. In a flowering plant, too, all 

 the cells do not continue to grow; many cells differentiate 

 and cease to grow and also some of the groups of meris- 

 tem remain dormant in axillary buds. Clearly the growth 

 curve can not continue to accelerate logarithmically, and 

 in later phases it must tail off ; the 1 'grand period" which 

 growth is said to exhibit is another way of stating this. 

 It will, however, be of great interest to us to see what will 

 be the form of the curve of growth during the early period 

 of development. 



The importance of this class of work has been realized 

 in Geneva, and detailed work is now being done under 

 the inspiration of Professor Chodat 8 in which the curve 

 not only of growth (fresh weight) but of the uptake of 

 all the separate important elements in selected plants is 

 being carefully followed. 



With plants grown in the open, climatic disturbances 

 must occur. We shall therefore figure a curve for the 

 fresh weight of a maize plant grown in water-culture. 

 This is prior to the Geneva work, and due to Mile. Stef- 

 anowska, 10 who has studied also the growth-curves of 

 small animals. The first phase of the curve, lasting some 

 fifty days, shows strictly uniform acceleration, doubling 



