98 THE CARBOHYDRATES 



members of this same class of plants are fairly constant starch 

 producers, e.g., Lilium tigrinum, Pontederia cordata, Ananas 

 sativa, Canna indica, Tradescantia virginica, Juncus communis, 

 and Alisma Plantago. There are many peculiarities in this 

 occurrence of starch in the Monocotyledons ; for instance, in 

 Scilla nutans it is absent, whilst in Scilla siberica it is quite 

 abundant ; further, the former plant, if fed with cane sugar in 

 a solution of suitable strength, does not form it, while, on the 

 other hand, starch-free plants of Scilla siberica under the same 

 treatment do form starch, the experiment, of course, being 

 carried out in the absence of light. In the plant starch occurs, 

 as is well known, in the form of variously shaped microscopic 

 bodies composed of concentric layers ; the granules have an 

 organized structure and possess the power of double refraction. 



Preparation of Starch, 



The method of preparation varies according to the source 

 employed. From wheat flour it may be obtained by stirring 

 up this material thoroughly with water, and allowing the mix- 

 ture to stand until the gluten contained in the flour undergoes 

 fermentation, when it dissolves and may be removed by wash- 

 ing. On a small scale the separation is most conveniently 

 effected by kneading some flour in a muslin bag which is held 

 under a stream of water. The starch granules are hereby 

 washed through the muslin, while the gluten remains behind 

 in the bag as a sticky grey mass. 



Starch may also be obtained from potatoes by macerating 

 them with water and separating the non-starchy material from 

 the starch by filtration. The starch is then allowed to settle at 

 the bottom of the water, when it is collected and dried. 



Purification. 



Malfitano and Moschkoff * give the following method for 

 the purification of starch : A one per cent colloidal solution of 

 starch is frozen and then allowed to melt. When melted, most 

 of the starch is deposited in a floccular precipitate, whilst the 

 clear liquid contains some starch and the greater part of the 



* Malfitano and Moschkoff: " Compt. rend.," 1910, 151, 817. 



