NOVISMBEE 6, 1908] 



SCIENCE 



629 



mass, and the catalytic acceleration of re- 

 action velocity, Professor Blackman pro- 

 ceeded to consider the broad phenomena of 

 metabolism or chemical change in the liv- 

 ing organism from the point of view of 

 these principles of chemical mechanics. 



Plants of all grades of morphological 

 complexity, from bacteria to dicotyledons, 

 have this in common, that throughout their 

 active life they are continually growing. 

 Putting aside the qualitative distribution 

 of growth that determines the morpho- 

 logical form, as a stratum of phenomena 

 above the fundamental one that we are 

 about to discuss, we find that this growth 

 consists in the assimilation of dead food- 

 constituents by the protoplasm, with a re- 

 sulting increase in the living protoplasm 

 accompanied by the continual new forma- 

 tion of dead constituents, gaseous COj, 

 liquid water, solid cellulose, and what not. 

 This continual flux of anabolism and 

 katabolism is the essential character of 

 metabolism, but withal the protoplasm in- 

 creases in amount by the excess of anabo- 

 lism over katabolism. 



Protoplasm has essentially the same 

 chemical composition everywhere, and in 

 the whole range of green plants the same 

 food materials seem to be required; the 

 six elements of which proteids are built are 

 obviously essential in quantity as building 

 material, but in addition small amounts of 

 Fe, Ca, K, Mg, Na, CI and Si are in some 

 other way equally essential. What part 

 these secondary elements play is still 

 largely a matter of hypothesis. 



Regarding metabolism thus crudely as if 

 it were merely a congeries of slow chemical 

 reactions, let us see how far it conforms to 

 the laws of chemical mechanics we have 

 outlined. 



If the supply of any one of these essen- 

 tial elements comes to an end, growth 

 simply ceases and the plant remains sta- 

 tionary, half-developed. If a Tropceolum 



in a pot be watered with dilute salt-solu- 

 tion, its stomata soon close permanently, 

 and no CO2 can diffuse in to supply the 

 carbon for further growth of the plant. 

 In such a condition the plant may remain 

 for weeks looking quite healthy, but its 

 growth may be quite in abeyance. 



In agricultural experience, in manuring 

 the soil with nitrogen and the essential 

 secondary elements, the same phenomenon 

 is observed when there is a shortage of any 

 single element. If a continuous though 

 inadequate supply of some one element is 

 available, then the crop development is 

 limited to the amount of growth corre- 

 sponding to this supply. Agriculturalists 

 have formulated the "law of the mini- 

 mum," which states that the crop de- 

 veloped is limited by the element which is 

 minimal, i. e., most in deficit. Develop- 

 ment arrested by "nitrogen-hunger" is 

 perhaps the commonest form of this. All 

 this is, of course, in accordance with ex- 

 pectation on physical-chemical principles. 

 The quantity of anabolic reaction taking 

 place should be proportional to the amount 

 of actively reacting substances present, and 

 if any one essential substance is quite ab- 

 sent the whole reaction must cease. It 

 therefore seems clouding a simple issue 

 and misleading to say of a plant which, 

 from the arrested development of nitrogen- 

 hunger, starts growth again when newly 

 supplied with nitrogen that this new 

 growth is a response to a "nitrogen stimu- 

 lus." It would appear rather to be only 

 the removal of a limiting condition. 



Let us now move on a stage. Suppose 

 a growing plant be liberally supplied with 

 all the thirteen elements that it requires, 

 what, then, will limit its rate of growth? 

 Fairy bean-stalks that grow to the heavens 

 in a night elude the modern investigator, 

 though some hope soon to bring back that 

 golden age with overhead electric wires and 

 underground bacterial inoculations. If 



