CARBOHYDRATES AND FATS 473 



The loss by respiration rapidly becomes more and more marked, and the 

 starch which disappears from the maize plants is used both in respiration and 

 in the formation of sugar and cellulose, for the fat alone does not suffice to 

 cover the loss by respiration or to produce the amounts of sugar and cellulose 

 which appear. In hemp seedlings fat is utilized for the formation of starch 

 and also of cellulose, the latter being possibly produced from the former, for 

 between the seventh and tenth day a large quantity of starch is consumed and 

 much less fat. 



Experiments of this kind indicate only the beginning and the end of meta- 

 bolism, but nevertheless they suffice to show that its course is by no means 

 always the same. Thus during the germination of the oily seeds of the cucumber 

 (Peters) and of Allium cepa (Sachs) glucose is formed abundantly, whereas 

 hardly any appears in seedlings of Cannabis sativa. Similarly, oil is formed from 

 glucose in the ripening seed of Ricinus (Sachs), but in the endosperm of Paeonia 

 mainly from starch (Pfeffer). Again, a beetroot forms cane-sugar, but the tuberous 

 roots of Dahlia and the tubers of Helianthus store inulin, from such carbo- 

 hydrates as glucose and starch. 



A few general remarks may be made upon the physiological relationships 

 of the more commonly occurring non-nitrogenous substances, but for a more 

 complete account the reader is referred to the literature already quoted. (On 

 cellulose, cf. Sects. 83 and 84.) 



Starch grains. These remain within the chloroplastids or leucoplastids in 

 which they were produced until they are dissolved and removed \ so that under 

 normal conditions they are never found lying free in the protoplasm or cell-sap 2 . 

 Even were the latter the case, the starch grains would not be lost, but might be 

 rendered soluble by the action of ferments, as occurs, for example, when fungi 

 are fed with starch. The latter moreover usually disappears from dying cells of 

 starch-forming plants. On the action and production of diastase, see Sect. 91. 

 The growth of starch grains will be discussed later. 



Starch grains are composed mainly or entirely of amylose, and usually turn 

 blue with iodine; but in certain cases, as in the seed-coat of Chelidonium, 

 Oryza, &c., they are mainly composed of amylodextrin, and other dextrins as 

 well, so that a red colouration is produced with iodine. These substances are 

 formed as intermediate products of diastatic action, so that starch grains which 

 redden with iodine may be regarded as having undergone partial conversion into 

 sugar. Certain forms of mucilage are perhaps composed of dextrins soluble in 

 water. Another product of diastatic action, namely maltose, apparently commonly 

 occurs in plants 3 . 



1 Cf. Sects. 53-55. Details and literature on starch, A. Meyer, Unters. iiber die Starkekorner, 

 1895. Estimations of the percentage of starch present in plants by Konig and by Ebermayer : cereals 

 contain from 50 to 70 per cent., potatoes 15 to 30 per cent., by dry weight. 



2 Pfeffer, Aufnahme u. Ausgabe ungeloster Korper, 1890, p. 177. Cf. Sect. 19. Starch may be 

 found in living tracheae, or in those filled by tyloses (Lange, Flora, 1891, p. 393). 



3 Detected in a few cases by Brown and Morris, Journ. of Chem. Soc., 1893, p. 662 ; Bot. 

 Zeitung, 1892, p. 465. [A few forms of plant mucus (pectin compounds combined with amylose?) 

 give a blue colouration with iodine, possibly owing to the presence of carbohydrates more or less 



