THE VEGETABLE CELL 299 



two or more hila, each with its concentric rmgs, and the whole 

 surrounded by several layers of the same material. In this 

 case the amyloplast has begun to form two or more grains at 

 points towards its exterior, and these in time have come into 

 contact. The further activity of the plastid has led to the 

 aggregation becoming surrounded by deposits or shells of starch 

 (fig. 652, B). 



In some cases the starch grains are of extremely curious 

 shape. They may be rod-like, or like dumb-bells with elongated 

 handles, as in Euphorbia. These are formed by plastids which 

 divide into two during the process of deposition of the starch 

 {fiff. 653). 



In many cells the starch grains are extremely minute and 

 occur in enormous numbers, as in the style of the Lily. These 

 specks are probably formed directly by the protoplasm, as no 

 plastids hiave yet been discovered in the cells of this tissue. 



Cotrijiosition and Chemical Characteristics of Starch 

 (O^iJjoOj),,. — The starch granule consists of the true starch- 

 compound and water. The starch-compound is again formed 

 of two substances, which are intimately blended together, 

 viz. granulose and starch-cellulose. The granulose makes up 

 by far the greater part of the starch-compound ; it is capable 

 of being dissolved out of the cellulose by saliva and dilute acids, 

 and it is to it that the starch granule owes the violet-blue 

 coloiu: which it assumes when treated with a solution of iodine. 

 The cellulose on the other hand, not being soluble, is left 

 behind as a skeleton, and is not coloured blue by the iodine 

 solution. 



Starch is insoluble in cold water, alcohol, ether, and oils. By 

 the action of boiling water it swells up and forms a mucilage 

 or paste ; if to this when cooled iodine be added, a deep blue 

 colour is produced ; but this colour is at once destroyed again 

 by the application of heat or alkalies. If starch be exposed to a 

 temperature of about 320° F. for a short time, it is converted 

 into a soluble gummy substance, called dextrin or British gum. 

 By the action of dilute sulphuric acid it is transformed into 

 sugar. The same change is brought about in the cells of the plant 

 by a peculiar nitrogenous body known as diastase, a member of 

 a group of bodies termed enzymes, which are of widespread 

 occurrence in plants and which wiU be spoken of later. 



Proteids. — We have already seen that the protoplasm of the 

 cell encloses in its meshwork varying quantities of the peculiar 

 nitrogenous material known as proteid. In some cells this exists 



