146 STARCHES. 



phyll in the light, be placed in the dark, it is again absorbed by the 

 living plant as seen in Spirogyra, etc. Although this is the general 

 rule, yet some tuberous plants — as the potato, where the tubers 

 contain an abundance of starch — seem to possess the property 

 whilst germinating of absorbing the starch of the tuber and again 

 depositing it, although no ray of light has ever reached the plant, 

 thus trying to put forth its powers. In perfectly dark cellars it is 

 not uncommon to find small young potatoes from the size of a pea 

 to that of a walnut, when the tubers have been left to germinate. 

 The shoots here are wonderfully elongated and quite white from 

 want of light and of the formation of green chlorophyll. As the 

 young tubers thus formed are always small and few in number, it is 

 very doubtful whether any further development of starch has really 

 taken place, but it is thus certain that after the starch of the tuber 

 has been rendered soluble it may be again deposited at least par- 

 tially in absence of chlorophyll and of light. 



As starch enters so largely into the food of man, it frequently 

 becomes necessary to distinguish between the starches, as derived 

 from various sources, in order to be able to state whether any 

 admixture may have been added to a given article. Thus, it 

 sometimes occurs that wheat-starch finds its way into pepper, 

 potato-starch partially replaces the more expensive arrowroot, and 

 rice has been made up to resemble sago or tapioca. 



These adulterations can only be discovered by examining the 

 intimate structure of the article by the microscope, and in order to 

 do this it is necessary to note — (i) Shape and size of granule. 

 (2) Position and shape of hilum. (3) Position and clearness of 

 concentric rings. (4) Facility with which the granules polarise. 

 Granules of starch vary in size in different samples, from 1-5, 000th 

 of an inch — as in liquorice, ipecacuanha, and rice — to the 1 -200th 

 of an inch in tous les mois. Now, although from the natural growth 

 of starch-grains we may find in any sample of a large variety a 

 number of very small grains, yet on the whole the size may be 

 fairly relied on \ at least to the extent that in each species the size 

 of the grains will never be larger than a certain maximum. 



In this microscopic examination of starches we may divide 

 them into certain groups : — 



I. — Oval, more or less, and with hilum and rings well visible. 



