PLANT CELL GROWTH AND NUTRITION 455 



tions in which they may occur (Tables II and III), with the expendi- 

 ture of metabohc energy in a system which functions dynamically as a 

 working machine, is essentially a contribution of the second quarter of 

 this century. 



The interrelations of form and function have been the traditional 

 meeting ground of physiologists and morphologists, and from Haber- 

 landt to J. H. Priestley attempts to interpret the structure of cells, 

 tissues, and organs in relation to their behavior and role inspired the 

 movement which became known as physiological plant anatomy. Prior 

 to this, the general responses of plants to external stimuli, early attrib- 

 uted to a universal property of living material called "irritability," 

 paved the way for the modern work on hormones and growth-regulat- 

 ing substances of all kinds. All this had its basis in the cell doctrine, 

 which led to the development of general and cell physiology as investi- 

 gators applied their then-available chemical and physical knowledge to 

 problems of cells and of protoplasm and later of their respective inclu- 

 sions. But enzymology, intermediary metabolism, and the standpoints 

 of "comparative biochemistry" are essentially creations of this century, 

 while the current descriptions of tlie structure of organelles and of 

 macromolecules at the submicroscopic level could only proceed as the 

 electron microscope and other physical techniques became available. 

 Thus the old problems of form and fimction are carried down to much 

 lower orders of magnitude. 



The triumphs of biochemistry and biophysics, which have helped 

 to describe in ever-greater detail the molecules that build the struc- 

 tures of cells, the metabolites, the enzymes, the co-enzymes that medi- 

 ate their reactions, and the reversible metabolic cycles which permit 

 the flow of groups, or radicals, of hydrogen or of electrons through the 

 metabolic machine, may now divert attention from what seems to be an 

 important and somewhat neglected topic. This is to know how cells and 

 organisms function as organized systems: i.e., how the various systems 

 that have been described, often at the molecular lexel, can be put to- 

 gether to make a harmonious, coordinated whole. It is as though in 

 modern cellular biology we have much knowledge of what might be 

 called the "unit operations" but know relatively httle about the over-all 

 design of the "factory" in which they occur and still less about its over- 

 all management. 



As early as 1905 and in a prescient passage, F. F. Blackman con- 

 ceived of the cell as a "congeries of enzymes," a "colloidal honeycomb 

 of catalytic agents," etc. Again, General Jan Christian Smuts— soldier, 

 statesman, botanist, and philosopher in the grand tradition of the late 

 nineteenth and early twentieth century— used a plant cell to illustrate 

 his doctrine of "Holism," although he lacked the enormously extended 

 modern knowledge, since he wrote in 1926. According to this doctrine. 



