136 STATE HOETICULTURAL SOCIETY. 



but often in a horizontal position and rarely upward. In such place (in 

 damp air) roots manifest a tendency to make one or more coils near the 

 tip. Roots of squashes, dandelions, in fact of almost any of our cultivated 

 plants, soon shorten after they have reached down or sidewise into the 

 soil. It is queer that they should do so, but this act causes the roots to 

 tighten on every side and hold the plant above the ground in an upright 

 position, as wet ropes shorten and hold a mast firmly in its place. The 

 main function of roots of our orchard and garden crops is to absorb (by 

 the root hairs in most cases) water from the soil, and this water holds in 

 solution small quantities of earthy matter, and some gases to a limited 

 extent. The water taken is mostly known as hygroscopic water, and not 

 stagnant nor free water; i. e., the hairs absorb water that merely wets the 

 surface of the particles of soil in which there are numerous irregular air 

 spaces. The microbes in the bunches on clover roots enable them to get 

 nitrogen, which the plant absorbs. 



In autumn, when the leaves die, most or all of the smallest rootlets 

 perish, and in spring a new supply is put forth when the buds spread out 

 their leaves. Some roots above ground hold a plant fast to a tree or a 

 wall. 



STRUCTURE AND OFFICE OF LEAVES. 



The green leaves and other green parts of our common plants are spread 

 out to the sunshine and the air. The leaf of a beet and of many other 

 plants has a layer of cells covering it above and below known as the epi- 

 dermis. These cells, soon after they acquire their growth, contain air 

 only, or but little other matter. They serve to protect the more delicate 

 cells within from sudden changes of temperature and help retain the 

 moisture which might otherwise escape too rapidly. In dry, hot climates, 

 leaves exposed to the sun are covered with epidermal cells of extra thick- 

 ness, and not unfrequently with two or more layers on the upper surface. 

 In the shade or in more moist climates the epidermis is less firm in tex- 

 ture. On the lower side of most leaves, and sometimes also on the upper 

 side, are large numbers of minute mouths, each consisting of two lips. In 

 moist air the lips open and allow surplus water to evaporate from the 

 plant, and in dry air they generally close to help retain moisture. On the 

 surface of leaves there is often a glaucous or waxy substance which pre- 

 vents the rain from penetrating the leaf. Water, to no appreciable extent, 

 is absorbed by leaves. In a dry time a plant wilts because the roots fail 

 to supply sufficient moisture, and on the approach of rain or moist air 

 leaves revive, because the roots can supply them with an abundance of 

 water. Inside the leaves, the cells contain protoplasm which is colored 

 green by a minute portion of coloring matter known as chlorophyll. In 

 these green cells take place some complicated changes, analagous to the 

 digestion of food in the stomachs of the higher animals; also of breathing 

 by lungs. Surplus water and oxygen escape through the small mouths, 

 the stomata above referred to. The framework of the leaves contains what 

 are called veins or nerves, for want of better names, although they do not 

 perform the function of veins or nerves in animals. Leaves do their work 

 of assimilation in the daytime. They wear out or become useless in one 

 season or in less time; in some instances they endure for more than one 

 year, in which case plants are termed evergreen. These leaves are usually 



