320 PHYSIOLOGY AT THE FARM. 



Starch. Starch is known by the several names, amylum, 

 fecula, and farinaceous matter. It is largely distributed 

 throughout the vegetable kingdom, or throughout the crypto- 

 gamic, the endogenous, and the exogenous subdivisions of that 

 kingdom viz., in the thallus or cellular expansion in lichens 

 and other cryptogams bearing the fructification, and of the 

 rest in the roots, stems, tubercles, fruits, and seeds. 



The starch in the vegetable kingdom is organised. Minute 

 microscopic particles, rounded or elliptical, flask-shaped or 

 mullar-shaped, or polyhedral. These grains have a laminated 

 texture, exhibiting a series of concentric layers or membranes, 

 the outermost of which is the thickest or the. firmest. Owing 

 to the pressure of these layers starch grains show rings or rugae 

 on their surface, as is evident in the grains of " tous les mois " 

 and of potato-starch. When examined with a microscope 

 magnifying to the extent of three hundred or four hundred 

 diameters, the grains are seen to consist of flattened ovate 

 granules of very uniform size in the same plant, but of vary- 

 ing magnitude in different plants. The concentric rings ob- 

 servable have led some to conjecture that there is a deposition 

 of successive layers of starchy matter within an external en- 

 velope ; but the latest evidence seems to show that the rings 

 are occasioned by a plication of the envelope itself. What is 

 called the hilum in the starch grains is a circular spot, and 

 sometimes two or three such spots, believed to mark the point 

 of attachment of the grain to the cellular tissue of the plant 

 from which it was developed. To show the structure of starch 

 grains, some are placed in contact with a drop of concentrated 

 solution of chloride of zinc (tinged with a little free iodine) in 

 the field of the microscope. Till a little water is added no 

 change takes place ; then they become of a deep-blue colour, 

 gradually expanding ; around the globule a frill-like plicated 

 margin is developed, opening out by degrees. The plications 



