204 



PHOTOSYNTHESIS 



1 CH2.0H 



I 



2 CH.OH 



I 



3 CH.OH 



I 



4 CH.OH 



I 



5 CH.OH 



I 



6 CO.H 



That the monosaccharides found in plants are not confined to five and 

 six carbon atom sugars, as was supposed for a long time, has become evi- 

 dent from the discovery of La Forge and Hudson of naturally occurring 

 heptoses. These authors report the presence of a seven carbon atom 

 sugar, sedoheptose, in the leaves and stalks of Scdiim spcctabile. Sedo- 

 heptose is an alphaketoheptose, the structural constitution of which has 

 not yet been definitely established. It is not fermentable, reduces Fehling's 

 solution, and, when heated with dilute acids, forms an anhydride ; this 

 anhydride does not reduce. This sugar is related to the naturally occurring 

 heptitol, volmetiol.^^ 



Another heptose, d-mannoketoheptose, has been isolated by La Forge ^'' 

 from the fruit, avocado, Persea gratissima. This is also a non-fermentable 

 sugar. From the same source has been obtained the heptitol, perseitol, 

 which Fischer showed to be the alcohol obtained by the reduction of 

 a-mannoheptose. 



k. The Conjugated Carbohydrates. 



The monosaccharides are the building blocks of which the more 

 complex carbohydrates are composed. The body of a plant is made up 

 largely of these complex carbohydrates, more especially cellulose. But 

 not only the structural elements of a plant and the conducting systems, 

 but also the leaves and centers of photosynthetic activity contain relatively 

 large quantities of the conjugated carbohydrates. In general when the 



•^La Forge and Hudson, Jour. Bio. Chcm., 30, 61 (1917) ; 42, 367, 375 (1920). 



"La Forge, Jour. Bio. Chcm., 28, 511 (1917). Maquenne, Conipt. rend., 107, 583 

 (1888). Fischer, Ber. chem. Cos., 23. 936 (1890). Fischer and Passmore, ibid., 

 23, 2226 (1890). 



