Structural Botany : Photosynthesis. IV. 



ANABOLISM expresses the building of living plasma; initial stages only are 

 open to experimental observation, as : 



Photosynthesis, more usually restricted to the elaboration of carbohydrate 

 from CO 2 and H 2 O in the presence of solar radiation: experimental observations 

 show that on exposure to sunlight under suitable conditions starch-grains, which can 

 be tested by Iodine solution, appear in the chloroplasts : e. g. in two hours in Funaria 

 leaf, and 5 minutes in cells of Spirogyra. Such general facts first noticed by Sachs 

 (1862): The presence of chlorophyll is apparently as essential as that of light; 6 fac- 

 tors in all : 



(a) General factors for healthy metabolism of the plasma : 



(1) Water-supply for aqueous plasma. 



(2) Temperature with max. and min. range ; opt. about 80 F. 



(3) Oxygen-supply, generally conceded from conceptions of katabolism. 

 (ft) Special factors of the chlorophyll-mechanism : 



Chlorophyll in special plastids (chlorophyll-corpuscles, chloroplasts). 

 CO 2 supply as free gas of the atmosphere ; 3 parts in ten thousand. 

 3) Light of the Sun, of optimum diluted intensity (white-cloud illumination). 



Chlorophyll, a green pigment, soluble in oil on surface of chloroplast ; general 

 constitution fairly known (Willstatter, 1910), containing Mg, but no Iron ; extracted 

 by solvents as spirit, with other substances, as a more or less complex mixture, giving 

 a similar green solution, fluorescing blood-red, and presenting a characteristic absorp- 

 tion-spectrum, with several bands (7) ; the chief one in the red (B ^ C) ; a faint band, 

 C ^ D; one in the green (beyond D); a faint one before E, and all beyond F (violet end) : 

 i. e. certain light is absorbed (mainly red), much is reflected as green. Hence infer 

 red light is the optimum for photosynthesis : but all rays may be used, as under trees, 

 a soft green light being residual. 



Bacterium-method of Engelmann (1882) gives a means of checking the evolu- 

 tion of Oxygen as part of the work done. Depends on the fact that certain Bacteria 

 are motile only in presence of free O 2 : on placing a green algal filament in the field 

 of a micro-spectrum, bacteria congregate in the region of maximum evolution, and 

 a curve may be drawn. This again gives most active decomposition in the red (B J C, 

 wave length 660-680 /x/x), with less action in the rest of the spectrum. Hence con- 

 clusion accepted that primarily energy of red light is converted into chemical work, 

 with evolution of O 2 and production of Carbohydrate from CO 2 and H 2 O. Experi- 

 mental gas-analysis shows that there is no change of volume involved ; i. e. for an 

 equal vol. of CO 2 absorbed, equal vol. of O 2 is set free ; 



The Theoretical Result may be provisionally expressed in the form: 



OfT 

 O : C : O + H-O-H = O 2 + ]C' ^ the suggestion being that O 2 comes jointly from CO 2 



and H 2 O ; the Carbon atom comes into association with the ions of water, with 

 the possibility of attaching indefinitely similar (CHOH)" groups in chain-forma- 

 tion. A suggestive formula involving 6 such groups, stabilized in molecular form, is 

 given for glucose, as the simplest monosaccharide found free in the plant : 

 CH 2 OH-CHOH-CHOH-CHOH-CHOH-COH 



One such group would stabilize as H-COH (Formaldehyde), invariably associated 

 with the chlorophyll-mechanism. Monosaccharide groups condense with separation 

 of H 2 O to form polysaccharides of (C 6 H 10 O 5 ) W class, to which starch is ascribed. 



Hence the appearance of starch -granules in a chloroplast implies the end of 

 a long sequence of actions in which starch, itself insoluble, is off the main line of 

 synthesis, and so far a by-product, expressing excess of carbohydrate production, 

 rather than the actual amount formed. Sugars as monosaccharides are probably 

 nearer the main line of proteid-synthesis : disaccharides (as cane-sugar) are similarly 

 to be regarded as by-products. These have diminished osmotic value, and starch 

 has none at all, hence the meaning of their production may be the avoidance of 

 injurious osmotic action in the cell-sap of the working units. All further production 

 of starch, celluloses, ligno-celluloses, benzene-derivatives, and terpenes, may be 

 regarded as roughly following a sequence of progressive depletion and substitution 

 of OH groups in an anhydro-aggregate of such primary monosaccharides. 



