CARBOHYDRATES AND FATS 475 



in the storage-cells must be extremely high : thus 25 per cent, of glucose 

 is equivalent to a pressure of 37 atmospheres, provided the glucoses are present 

 in the living plant as such (Sect. 24), whereas a similar percentage of cane-sugar 

 would only generate about half this pressure. 



All three forms of sugar may be metamorphosed into one another, and may 

 be produced from various substances ; but when cane-sugar is produced after the 

 conversion of oil or starch, it is impossible even in the latter case to be certain 

 that the polysaccharide is formed directly by the condensation of invert-sugar. 

 Diastase cannot aid in producing cane-sugar directly from starch, for the pro- 

 ducts of diastatic action are dextrose and maltose, whereas none of the laevulose 

 which comes from the inversion of cane-sugar ever appears 1 . Dextrose and 

 laevulose are certainly not always produced by the disintegration of cane-sugar, 

 and hence the relative amounts present of each may vary indefinitely. Whether 

 any preference exists for either form of sugar is uncertain, but experiments with 

 fungi how that sometimes dextrose, at other times laevulose, is consumed with 

 greater avidity' 2 . 



Galactose. A. Meyer 3 has detected this form of sugar in various members 

 of the Sileneae. Galactose and glucose are the products of the hydrolysis of milk- 

 sugar, but it is very doubtful whether the latter ever occurs in plants. 



Inulin is found especially in the Compositae, but it occurs also in many 

 of the Campanulaceae, Lobeliaceae, and Stylidiaceae, in Drosophyllum (Penzig), 

 and in Neomeris and a few of the Siphoneae (Cramer) 4 . It occurs mainly in 

 subterranean organs, but also in small amount in the sub-aerial stems and leaves 

 of certain plants B . Inulin apparently functions as a general rule as reserve- 

 material, but according to G. Kraus it may also appear in the translocatory 

 channels. Prantl found that inulin is often absent from the annual Compositae, 

 while it commonly disappears from biennials during flowering. It is retained in 

 dissolved form in living cells even at low temperatures or when the cell-sap 

 is concentrated by plasmolysis, but after death granular or sphaerocrystalline 

 precipitates are formed 6 . Inulin is soluble only with difficulty, and it is uncertain 

 whether the living cell contains a super-saturated solution or whether it is held in 

 solution by other means. 



It is also unknown whether a hydrolytic enzyme always takes part in the 

 mobilization of this variety of carbohydrate, for diastase and the invertase of yeast are 



1 [Gmss (Ber. d. D. Bot. Ges., xvi, 1898, p. 18) states that in barley seedlings cane-sugar is 

 formed from dextrose, and cellulose and starch from the former.] 



2 For literature see Pfeffer, Jahrb. f. wiss. Bot., 1895, Bd. xxvill, p. 227. 



3 A. Meyer, Bot. Zeitung, 1886, p. 106. 



* Tollens, 1. c., 1888, p. 199; 1895, p. 233; Prantl, Das Inulin, 1870 ; G. Kraus, Bot. Zeitung, 

 1877, p. 330; Vochting, Bibliotheca Botanica, 1887, Heft 4, p. 52, and Sitzungsb. d. Berl. Akad., 

 1894, p. 711 5 Eh.rb.ardt, Bot. Centralbl., 1894, Bd. LX, p. 207 (Leufojum); Penzig, Unters. iiber 

 Drosophyllum lusitanicum, 1877 ; Cramer, Ober Neomeris u. Cympolia, 1887, pp. 16, 26 (Sep.-abdr. 

 a. Denkschr. d. Schweiz. Naturf.-Ges., Bd. xxx). 



5 G. Kraus; Vochting, I.e.; Pistone de Regibus, Bot. Centralbl., 1883, Bd. XIII, p. 365; 

 Beauvisage, Bot. Jahresb., 1888, p. 47 (in Jonidium); G. Meyer, Ber. d. Bot. Ges., 1896, 



P- 355- 



*. Cf. Ziminermann, Mikrotechnik, 1892, p. 76. 



