346 



NATURE 



[M 



ARCH 1 6, 1922 



visible region by chlorophyll is not sufficient to induce 

 the complete reaction, since 150,000 calories per 

 gram-molecule is almost exactly one quantum per 

 molecule at A. = 2oo/x/i,. Certain quantitative experi- 

 ments have shown that a possible explanation of this is 

 to be found in the fact that the carbonic acid is partly 

 activated by combination with the chlorophyll. 

 Alternatively, it is possible that, whilst one quantum 

 of energy at A = 2oo/>i/x is required for the complete 

 reaction with the escape of free oxygen, one quantum 

 of visible light as absorbed by the chlorophyll is suffi- 

 cient to induce the reaction 



Chlorophyll A + H^COs = chlorophyll B + CHjO . 

 It is scarcely necessary to point out that either of 

 these alternatives amplifies the principle of photo- 

 catalysis as previously defined. In either case the 

 completion of the reaction, whereby the oxygen is 

 abstracted from the chlorophyll B and transpired into 

 the atmosphere, must require a further supply of energy. 

 This second amount of energy is doubtless absorbed by 

 the carotin and xanthophyll, the absorption bands of 

 which lie in the visible region and between those of 

 chlorophyll, so that each can absorb visible light 

 simultaneously and independently. This suggested 

 explanation is now being investigated. 



Reference may be made to some other work now in 

 progress at Liverpool which has already given most 

 promising and suggestive results. By the action of 

 ultra-violet light on aqueous solutions of formaldehyde, 

 several hundred grams of concentrated sugar syrup have 

 been prepared. Analysis of this syrup has shown that 

 the sole products of the polymerisation are hexoses, no 

 trace of a triose or pentose having been found. This 

 result is very striking in view of the greater possibiUty 

 on the kinetic theory of the formation of sugars con- 

 taining fewer than six carbon atoms. There can there- 

 fore be no possible doubt that the sole products of the 

 polymerisation of the activated formaldehyde as photo- 

 synthetically produced in the living plant are also 

 hexoses. Not only does this afford a ready explanation 

 of the storage of starch in the chloroplast during the 

 period of photosynthetic activity and its subsequent 

 hydrolysis to hexoses, which are utilised by the plant 

 in later syntheses, but it also establishes the fact that 

 pentoses must be formed from hexoses, possibly through 

 furane compounds; further, it opens the door to 

 most promising theories of the synthesis of other plant 

 products, every stage of which is attractive in its 

 simplicity. 



Then, again, there is the question of the production 

 of the various nitrogen compounds in the plant, which 

 is one of considerable interest, since it would seem that 

 the principal source from which the plant derives its 

 nitrogen is potassium nitrate. It is well known that 

 metallic nitrates are readily converted to nitrites by 

 material catalysts as well as by ultra-violet hght. 

 Baudisch has shown that an aqueous solution of 

 potassium nitrite and methyl alcohol, on exposure to 

 ultra-violet light, gives formhydroxamic acid, the 

 alcohol first being converted to formaldehyde. This 

 has been confirmed at Liverpool by investigation of 

 the action of ultra-violet light on aqueous solutions of 

 potassium nitrate or nitrite containing formaldehyde, 

 and it has been proved that an activated molecule of 

 formaldehyde combines with a molecule of potassium 

 nitrite according to the equation CH20 + KN02 = 

 CH(OH) : NOK + 0, since the reaction takes place 

 only in the light. It has also been found that if the 

 activated formaldehyde is in excess formhydroxamic 

 acid and hexoses are simultaneously and independently 

 produced. This condition is doubtless that which 

 obtains in the plant, and it may be concluded that 

 the two syntheses take place in the leaf without mutual 

 influence. It is worthy of note that the photosynthesis 

 of formaldehyde and the synthesis of formhydroxamic 

 acid are both accompanied by the setting free of oxygen. 



Experiments are also in progress on the reaction 

 between activated formaldehyde and ammonia, and 

 although these are not yet complete, they have already 

 established the great reactivity of activated formalde- 

 hyde towards ammonia. Whatever, therefore, may be 

 the starting point on the nitrogen side, potassium 

 nitrate or ammonia, there is no question that, in the 

 presence of activated formaldehyde such as is produced 

 photosynthetically in the plant, compounds are 

 formed in which carbon and nitrogen are united, thus 

 securing the first step towards protein, pyrrole, and 

 alkaloid synthesis. 



Finally, one very important deduction may be made. 

 The sole photosynthetic process in the living plant 

 would seem to be the production of activated formalde- 

 hyde from carbon dioxide and water. These activated 

 molecules either polymerise to hexoses or react with 

 potassium nitrite or ammonia. Any further reactions 

 are not photochemical except in so far that the first 

 synthesised nitrogen compounds combine with more 

 molecules of activated formaldehyde to give complex 

 nitrogen derivatives. 



The Migration of British Swallows. 



By Dr. A. Landsborough Thomson, O.B.E. 



" Sister, my sister, O fleet sweet swallow. 

 Thy way is long to the sun and the south." 



Swinburne. 



T^ROM time immemorial the Swallow {Hirundo 

 ^ rustica, Linn.) has been a proverbial type of 

 sumrner visitor to our northern lands, but age-long 

 familiarity with the fact of its seasonal appearance 

 and disappearance has not served to bring us complete 

 knowledge or understanding : there are many secrets, 

 both matters of fact and questions of interpretation, 

 to which we have as yet no clue. Nevertheless we are 

 NO. 2733, VOL. 109] 



in a better position to appreciate the problem than were 

 Gilbert White and his contemporaries, who were 

 obsessed with the idea that hibernation, particularly 

 in regard to this species, might play an important part 

 as an alternative to migration. White was particu- 

 larly influenced by the frequent phenomenon of the 

 few " early swallows " which appear some time before 

 the main contingents arrive, and are no more seen if 

 wintry weather should recur in the meantime. The 

 theory of hibernation dies hard even to-day, and every 

 now and then some imperfect piece of evidence in its 



