26. Water In Living Plants

Water constitutes a large proportion of the weight of all living plants, especially during the period of active growth. The cured hay, as any farmer's boy knows, weighs much less than did the green grass when it was cut, and this loss in weight is due almost wholly to evaporation of water from the tissues of the plant under the influence of the sun and wind. This water, which is contained in the tubes and inter-cellular spaces of the stalk or leaf, is exactly the same chemical compound as pure water found anywhere else, and has no more value for food, excepting that it is pure and is not subject to the contamination which sometimes occurs in streams and wells. There is no such thing as the so-called

"natural" water of plants which has a peculiar nutritive value or function. Vegetation water should be distinguished from sap or plant juice. Sap is more than water; it is water holding in solution certain substances such as sugars and mineral salts. When the plant is dried, these soluble compounds do not pass off, but remain behind as part of the dry matter.

27. Proportion Of Water Varies

The proportion of water in plants varies greatly in different species, and in some species according to the stage of growth or the surrounding conditions. These facts have more importance than is generally recognized, because the food value of vegetable substances is influenced by the proportion of dry matter. It is always necessary to know the percentage of water in vegetables and fruits before we can estimate their worth as food.

The variations in water content of the living tissues of different species of plants or parts of plants, as well as its large proportion, is well illustrated by the following average figures: -

Table VI. Water In Green Vegetables

28. Much Water In Immature Plants

Immature plants contain more water than older or mature ones. Young pasture grass is more largely water than the same plants would be after the seed is formed. This fact is consistent with the very rapid transference of building material during the active stages of growth. Analyses of samples of timothy grass cut at the Maine State College in 1879, and at the Pennsylvania State College in 1881, show the marked influence of the stage of growth upon the water content of the living plant: -

What is true of timothy is probably true of all vegetables in the perfectly fresh state.