PLANT PHYSIOLOGY 383 



in its growth. Attention was drawn to the remarkable 

 losses of potash and nitrogen from the plant at an early stage 

 in development. 



Boysen- Jensen (" Studies in the Production of Matter in 

 Light- and Shadow-plants," Bot. Tidsskr., xxxvi, Heft 4, 

 191 8, p. 219) has compared the percentage production of dry 

 matter in a typical sun-plant {Sinapis alba) with that in a 

 typical shade-loving plant {Oxalis acetosella). The growth of 

 the plant has been calculated as the difference between income 

 and expenditure, the gain in dry-weight being the result of 

 photosynthesis and salt-uptake, the loss in dry-weight being 

 due to the respiration of the various parts of the plant and to 

 leaf-fall, etc. 



Brenchley (" On the Relations between Growth and the 

 Environmental Conditions of Temperature and Bright Sun- 

 shine," Ann. Appl. Biol., vi, 1920, p. 211) has investigated 

 the relation of temperature and sunshine to the rate of growth 

 of garden peas grown in water-cultures. The rate of growth 

 has been expressed per unit dry-weight. It was found that 

 during the early seedling stage the rate of growth was associated 

 with relatively warm days and nights, bright sunshine having 

 little significant effect. During the later period the growth-rate 

 was associated strongly with sunshine and warm days, but not 

 significantly with night temperatures. 



On the basis of measurements of the height of sunflower 

 plants made at weekly intervals. Reed and Holland (" The 

 Growth-rate of an Annual Plant Helianthus," Proc. Nat. 

 Acad. Set., V, 1920, p. 135) have concluded that the growth-rate 

 of these plants approximates closely the course of an auto- 

 catalytic reaction as expressed by the formula 



dxjdx = Kx {a — x), 



in which a = the initial quantity of material subject to trans- 

 formation, X = the amount transformed at time /, and k = a 

 constant. They have suggested that the close agreement of 

 the actual mean height of the plants with that required by the 

 equation of autocatalysis may indicate that the growth-rate 

 is governed by constant internal factors rather than by external 

 factors. As the result of a quantitative study based upon 

 length measurements of seventy selected shoots of apricot-trees, 

 Reed (" The Dynamics of a Fluctuating Growth-rate," Proc. 

 Nat. Acad. Sci., vi, 1920, p. 397) showed that the growth of 

 the shoots followed a definite, though fluctuating, rate. The 

 maximum rate was exhibited soon after the season's growth 

 began, and fell off with some regularity to the end of the season ; 

 but three distinct intra-seasonal cycles of growth were ap- 

 parent. The growth in each cycle closely resembled the rate 



