A crystal of any of these substances will =grow= if placed under proper conditions. Thus, if a crystal of common salt is hung by a thread in a saturated solution of salt, which is exposed to the air, so as to allow the water to evaporate slowly, the molecules of the salt which is left behind and can no longer be held in solution, deposit themselves on the crystal in regular order and increase its size without changing its form. And, in this way, the small crystal may =grow= to a great size. The large crystals of sugar candy, which consist of sugar and water deposited from a strong syrup or saturated solution of sugar, grow in the same fashion, upon threads suspended in the evaporating syrup. In this mode of growth you will observe that the enlargement is effected by addition to the outside of the growing body; and moreover the matter which is added, namely, the salt or the sugar, already exists as salt in the brine or as sugar in the syrup.
56. =The Wheat Plant and the substances of which it is composed.=
Every one has seen a cornfield. If you pluck up one of the innumerable =wheat plants= which are fixed in the soil of the field, about harvest time, you will find that it consists of a stem which ends in a =root= at one end and an =ear= at the other, and that blades or =leaves= are attached to the sides of the stem. The ear contains a multitude of oval grains which are the =seeds= of the wheat plant. You know that when these seeds are cleared from the =husk= or =bran= in which they are enveloped, they are ground into fine powder in mills, and that this powder is the =flour= of which bread is made. If a handful of flour mixed with a little cold water is tied up in a coarse cloth bag, and the bag is then put in a large vessel of water and well kneaded with the hands, it will become pasty, while the water will become white. If this water is poured away into another vessel, and the kneading process continued with some fresh water, the same thing will happen. But if the operation is repeated the paste will become more and more sticky, while the water will be rendered less and less white, and at last will remain colourless. The sticky substance which is thus obtained by itself is called =gluten=; in commerce it is the substance known as =maccaroni=.