Dtcbmber 12, 1902.] 



SCIENCE. 



929 



sodium-hj-drogen-sulphite. Experimeiits on 

 a more comprehensive scale, conducted on 

 a variety of plants of different habits, are 

 needed before we can regard the process as 

 satisfactorily established. 



We have further to pursue the problem 

 by an inquiry as to the nature of the sugar 

 first formed. Certain considerations lead 

 to the \iew that it is probable that a sugar 

 of the aldose type must be accompanied in 

 the plant by a ketose. The hypothesis as 

 stated b}^ Bae.yer, and so far accepted till 

 quite recently, took no account of the latter. 

 The aldose grape sugar was the one always 

 suggested, and from this all others met 

 with have been held to be constructed. The 

 first appearance of a ketose, levulose, or 

 fruit sugar, has been associated with the 

 hydrolytic decomposition of cane sugar, it- 

 self constructed presumably from the grape 

 sugar. I fear sufficient attention has not 

 been paid to probability or to the normal 

 course of chemical action in framing our 

 hypotheses, for it is rather difficult to see 

 how some of the transformations somewhat 

 dogmatically affirmed can possibly take 

 place. I may refer in passing to the state- 

 ment that in the digestion of fat or oil 

 during germination part of it is converted 

 into starch or sugar. 



But to return to the construction of 

 sugar. The condensation of formaldehyde, 

 which can be brought about by the action 

 of basic lead carbonate, leads to the forma- 

 tion of several siigars, each yielding its 

 characteristic osazone. How far the con- 

 densation in the plant follows this is still 

 uncertain. It is quite possible that stages 

 intervene between formaldehyde and sugar 

 of any Mnd. It has been suggested that 

 formaldehyde in the presence of water may 

 under the conditions obtaining in the leaf 

 give rise to glycolaldehyde, a body which 

 forms sugar very readily indeed. The 

 formation of sugar directly from formalde- 



hyde is a much longer process and is at- 

 tended with greater difficulty. 



I may call your attention here to the views 

 of Brown and Morris traversing the theory 

 of the primary carbohydrate being grape 

 sugar. In their classical paper on the chem- 

 istry and physiology of foliage leaves they 

 have adduced strong evidence, based upon 

 analyses of the sugar-content of leaves of 

 Tropceoliim majus, that in this plant at any 

 rate the first sugar to be formed is cane 

 sugar. Whether or no this is the ease in 

 plants generally cannot at present be said, 

 though it appears from many considerations 

 probable. 



The part played by chlorophyll in photo- 

 synthesis has already been touched upon. 

 Remarkably little is known about chloro- 

 phyll itself. It has so far been found im- 

 possible to extract it from the chloroplast 

 without causing its decomposition, and 

 hence our ideas of its constitution, such as 

 they are, are based upon the examination 

 of something differing in some not well- 

 ascertained particulars from the pigment 

 itself. A remarkable relationship is known 

 to exist between the latter and iron, for 

 unless this metal is supplied to a plant its 

 chloroplasts do not become green. But 

 the condition of the iron in the plant is un- 

 certain; it seems probable that it does not 

 enter into the molecule of the pigment at 

 all. A remarkable series of resemblances 

 between derivatives of chlorophyll and 

 derivatives of hsematin, the coloring mat- 

 ter of haemoglobin, has been brought to 

 light by the researches of Schunck and 

 Marchlewski, which is very suggestive. The 

 same leaning towards iron is found in the 

 two pigments, but in the case of hiematin 

 our knowledge is further advanced than in 

 that of chlorophyll. The iron is known to 

 be part of its molecule. It can by appro- 

 priate treatment be removed, and a body 

 known as hcematoporphyrin is then formed, 

 which presents a most striking similarity 



