10 



Elementary botany 



being CoH,„05. It differs from it, however, in many of its 

 properties. It is insoluble in cold water, but swells up very 

 strongly on the addition of boiling water, forming a paste. It 

 is readily turned a dark blue by the addition of iodine. As 

 this blue colour, however, is removed by heat, the starch re- 



FlG. 7.— Various forms of starch grain from the Potato. 



quires to be cold, or nearly so, for its production. Exposed to 

 heat for some time, or to dilute sulphuric acid for a shorter 

 period, starch is converted into dextrine or British gum. 



Starch occurs in the plant in the form of granules varying 

 in their size. Amongst the smaller are those of Rice starch. 



Fig. 8.— I. Starch grain from the Scarlet Runner. II. a, h, Starch grains from Rye. 

 III. Starch grain from the stem of the Sarsaparilla {,Smiiax Sarsaparilla). 



which are frequently under ^^Vtj of an inch in diameter, whilst 

 those of the ' Tous-les-mois ' are often as much as ^^i^ of an 

 inch in length. In external form they vary very much, but 

 they usually present a central portion, the hilum, or nucleus, 

 round which the starch substance is arranged in concentric 



