18 CHEMISTRY OF PLANTS. 



B. Many smaller granules grown together upon one larger one. 



22. In the pith of Sagus Rumphii, &c., generally in the sago. 



Starch is the most generally distributed substance in the vegetable 

 kingdom. I am not acquainted with any plant which does not, at some 

 season of the year, at least at the period when vegetation is inactive, 

 contain more or less starch, frequently only in individual granules in the 

 cells, and frequently entirely filling them in grains of the most different 

 size. The starch granules adhere quite adventitiously, by means of mu- 

 cus, to the cell-walls. The umbilicus (hilum), by which the starch gra- 

 nules are said to be attached to the wall of the cell, is an error on the 

 part of Turpin. The largest granules do not appear to exceed 05 of 

 a line in their longest diameter. The starch is mostly readily obtained 

 by bursting the cellular tissue, and by washing it from the plant ; occa- 

 sionally, however, it cannot be thus obtained, as, for instance, when it 

 occurs combined with much mucus, as in Hedychium ; the starch in 

 Maranta arundinacea (Arrow-root) appears to be the purest. We 

 certainly do not say too much when we assert that starch constitutes 

 the most important, and the almost exclusive, food of two-thirds of all 

 mankind. It is certainly contained in all plants, but not always in such 

 a manner as to be sufficient and suitable for nutriment, and sometimes, 

 too, indivisible from other unpalatable admixtures, as, for instance, in 

 the horse-chestnut. Certain parts of plants contain it in the largest 

 quantity, namely, the albumen of seeds (the Cerealia), the cotyledons of 

 the embryo (Leguminosce), the medulla, or pith of the stem ( Cycadece and 

 PalmcB) * bulbs (Liliacece) f, the tubers, root-stocks, and roots of very 

 different families. J It occurs in smaller quantities in the bark and the 

 alburnum of trees in winter, whence the inhabitants of the Polar regions 

 are able to bake the bark of trees as bread. 



I must not omit to make mention of an error, which is unfortunately 

 too often repeated, and which may thus lead to much confusion, especially 

 in physiology. Decandolle believed that he had proved that 100 Ibs. of 

 potatoes would yield 10 Ibs. of starch in August, 14^ Ibs. in September, 

 14^ Ibs. in October, 17 Ibs. in November, 13J Ibs. in April, and again 

 10 Ibs. in May. From this it was concluded that the quantity of the 

 starch in the potato increased and diminished again during this interval 

 of time, a most erroneous idea, which has unfortunately been too often 

 repeated in recent times. It may, however, easily be conjectured that 

 such per-centage calculations can only give relative, but no absolute, 

 quantities for any plant, or part of a plant. Granting that Decaridolle's 

 calculation is correct, it says nothing more than that the weight of starch 

 gradually comes to stand in the same relation to the weight of the 

 potato as 10, 141, 17 ? & c ., to 100 ; but whether this changed relation is 

 to be sought in the change of the quantity of the starch, or in the dimi- 

 nution of other substances, is not even indicated. It is rather obviously 

 probable that in this case starch is neither formed nor destroyed, but that 

 the aqueous contents of the potato decrease by evaporation, and again 

 augment by absorption on the revival of vegetation. 



Historical Sketch. Starch was known even to the ancients. ("A/ziAoj/ 

 <Hia TO x w i' pv\ov Kara(TKvaecrdat, Dioscor.) Leeuwenhoek was the first 

 who examined it in plants, in wheat and beans ; and Stromeyer sub- 



* As sago, from Cycas revoluta, Sagus Rumphii, farinif era, &c. 

 f Lilium camtchaticum, in Greenland, &c., is a source of food. 



{ Potatoes, from Solanum tuberosum ; Cassava, from Jatropha Manihot ; Taroo, from 

 Arum esculentum ( Colocasia macrorhiza ?), &c. 



