38 THE SYNTHESIS OF CARBOHYDRATES 



Tropceolum, Vitis> Musa and other plants collected in the early 

 afternoon and early morning : he found that sucrose always 

 was more abundant than maltose and the other sugars identi- 

 fied ; he is in accordance with Brown and Morris regarding 

 the absence of pentose. Kylin * found that in general terms 

 the amount of glucose varies inversely as the amount of starch. 

 Sucrose is generally the most abundant sugar, especially in 

 sugar leaves, but Gentiana brevidens^ a sugar leaf, does not 

 contain any sucrose, whilst Tilia europ<za> a starch leaf, con- 

 tains much sucrose. 



In conclusion it may be said that leaves generally contain 

 sucrose, maltose, dextrose, and levulose, whilst the occurrence 

 of pentose is uncertain. 



With regard to starch, its occurrence and relationships to 

 sugar have already been considered,^ and since agreement 

 regarding the sequence of events in carbon assimilation which 

 culminate in the formation of sugar has not been reached, it 

 is not desirable here to discuss which is the primary sugar of 

 the synthetic process. 



Fats sometimes have been described as direct products of 

 carbon assimilation, more especially in plants, such as Van- 

 cheria, which have an abundance of fat-like substance in their 

 green tissues. The evidence for the contention is anything but 

 satisfactory, especially in view of the transmutation of carbo- 

 hydrate into fat in various plants and under the influence of 

 certain external conditions such as low temperature.* The 

 problem has been resuscitated by Meyer who describes the 

 presence of a colourless fluid of unknown composition and 

 having the physical properties of an oil which occurs in the 

 chloroplasts of Tropceolum. This substance, which is not a 

 fat, since it gives on distillation hexylenealdehyde, increases 

 with assimilation, and is considered by Meyer to be a definite 

 product of carbon assimilation. 



HYPOTHESES CONCERNING THE SYNTHESIS OF CARBO- 

 HYDRATE BY THE GREEN PLANT. 



With the problems associated with the march of events 

 from the initial carbon dioxide and water to the final carbo- 



* Kylin : id., 1918, loi, 77. f Vol. I. J See Vol. I. 



Meyer : " Ber. deut. hot. Gesells.," 1917, 35, 586; 1918, 36, 235, 674. 



