ON ORGANIC COMPOUNDS 97 



ports all the life of the seas. This is evident, because the spring 

 outburst of floating plant life occurs before there has been any rise 

 in the temperature of the sea water. The bronzing of the skin, 

 caused by exposure to bright sunshine, and the pigmentation of 

 human races in tropical climates, is almost certainly a protective 

 screen against these injurious rays, and Marshall Ward has pointed 

 out that the pigments of those micro-organisms and fungi which 

 can flourish in light always absorb these injurious rays, and allow 

 passage to the reds, greens, yellows, and oranges, which are not 

 injurious. Even blue and violet pigments occurring in nature, 

 when carefully examined spectroscopically, are found in many cases 

 to absorb the violet and shorter waved blues. 



The same is true of the colours of flowers, and even of the green 

 colouring matters of the foliage leaves, and it may well be that the 

 function of the chlorophyll, which usually occurs as a thin layer 

 like a skin over the chloroplast, is to temper and screen the light 

 for the really effective transformer lying underneath. 



The absence or great diminution of the blue and ultra-violet 

 rays in hazy or sunless weather may also be of great importance in 

 allowing the disease organisms of the higher plants to flourish un- 

 checked, and it is such weather in autumn .which often heralds the 

 outbreak of disease and blights. 



SUMMARY. 



The results recorded in this chapter may be placed under three 

 headings: (a) Photo-synthesis by inorganic transformers; (6) action 

 of sunlight and of ultra-violet light upon concentrated solutions of 

 formaldehyde; (c) the general formation of formaldehyde by the 

 action of light upon organic substances of biochemical origin. 



In the first section, the reactions of a number of inorganic systems 

 in presence of carbon dioxide and exposure to light are investigated, 

 and it is shown that certain of these can build up formaldehyde while 

 others are inert. The activity is shown to be related to the develop- 

 ment of an optimum degree of colloidality, and is not due to for- 

 mation of higher or lower oxides, but more probably to surface 

 condensation on interfaces. 



The second section deals with the condensation of formaldehyde 

 to form reducing substances leading to carbohydrates, and discusses 

 the conditions favourable for such condensations. The energetics 



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