258 The Carbo/ii/tf rates of the Mangold T.eaf 



which is stored in the root of the sugar beet is formed in the leaf of the 

 plant by direct photosynthesis and transferred as such to the root. 

 Girard's work, which from the quantitative standpoint was far more 

 complete than anything previously published, was apparently overlooked 

 by Brown and Morris in their 1893 paper. Girard's views were based 

 on nuniorous analyses which showed the roots to contain saccharose 

 only and no reducing sugar; reducing sugars, however, were present 

 in the stalks (petioles) and leaf tissue. The roots and petioles were 

 found to jiave the same composition by night as by day, but the pro- 

 portion of saccharose in the leaves was much greater — frequently twice 

 as great — at the end of a day's insolation than next morning, after being 

 several hours in darkness. The proportion of reducing sugars in the 

 leaves, however, was sensibly the same in the evening as next morning 

 and only increased as the plant developed. We shall discuss Girard's 

 data more in detail later. 



Since 1893 several papers have been published in which the formation 

 of carbohydrates in the leaf is considered. These may be di\'ided into 

 two classes: (1) Those whose authors favour the view that saccharose 

 is the first sugar formed in photosynthesis, (2) those in which the 

 hexoses are regarded as primary products, the saccharose as formed 

 later by synthesis either in the leaf or the root. AVe will briefly review 

 these two classes separately. 



1. Came sugar held to be formed directly. 



Went [1898] published observations on the distribution of reducing 

 sugars and saccharose in the unripe sugar cane. The value of these is 

 marred by the fact that, in the polarimetric estimation of cane sugar, 

 Went calculated the reducing sugars as dextrose. Although Went held 

 that cane sugar is the iirst formed sugar, he gives no experimental 

 evidence in favour of this view. Strohmer [1908] relied upon the fact 

 which was supposed to be established, first by Peligot and later by 

 Girard [1884], that the roots of the sugar beet contain no sugar but 

 saccharose ; he states that, in the beet, reducing sugars never occur in 

 the root, even in the early stages of growth. This, together with Girard's 

 observation that in the night the saccharose content of the leaf fell to 



leaves of several plante, e.g. Beta vulgaris, the grape vine {Vitis vinifera), potato, onion. 

 In the early stages of growth, Kayser's analyses show that the cane sugar in the leaves 

 is often greatly in excess of the lie.\ose.s, but later the proportion is increased. Kayser 

 actually separated cane sugar from the leaves of the vine in a crystalline condition and 



with [a]„ = r,2-<)°. 



