4 ELEMENTS OF BOTANY. 



it too has an external coating similar to that of the bean. Kemoving this, 

 the seed is found composed of a single body, marked on one side by a 

 longitudinal elevation (Fig. 6), instead of two similar parts as in the bean. 

 Buried in the earth, a kernel of corn absorbs moisture, the little elevation 

 on its side begins to elongate in an upward and downward direction (Fig. 8), 

 one extremity producing a cluster of roots, the other leaves (Fig. 9), the 

 seed itself remaining in the ground, and not borne above it as in the case 

 of the bean. 



Without tracing the history of these plants further, enough has been 

 shown to demonstrate that a seed is an embryo plant, as fully fitted for an 

 independent existence when placed under proper circumstances as is the 

 infant mammal when it issues from its mother's womb. The requisite 

 circumstances are in the one case, first of all, air to breathe, in the other, 

 moisture and seclusion from light. 



Having seen how a plant starts on its course of development from the 

 seed, we will now proceed to study the organs by means of which its various 

 functions are performed. 



THE ROOT. 



The root of a plant is its descending axis. In the vast majority of in- 

 stances it fixes the plant in position and gives support to the stem, but 

 not in all, for there are many aquatic plants whose roots are suspended in 

 the water, taking no hold upon the soil at the bottom. But even here 

 they give a certain amount of steadiness to the plant, and assist it in main- 

 taining a comparative equilibrium when the surface of the water is dis- 

 turbed by waves or currents. 



Roots present themselves in many different forms, and as these are 

 often made use of in botanical descriptions, it is necessary for the student 

 to familiarize himself with, at least, the leading ones. 



The simplest form of the root is that which grows directly downward 

 from the embryo, giving off but few lateral branches, and these of com- 

 paratively small size ; this is known as a tap-root. The beet, turnip 

 (Fig. 10), carrot, and radish, among herbs, are familiar examples in which 

 the tap-root attains a great development while its lateral branches are in- 

 significant. In many forest trees the main root penetrates the earth to a 

 considerable depth before lateral branches of important size are given off. 

 Such trees, however, never have tap-roots of as proportionably great size 

 as many herbaceous plants, for two reasons : plant food is more abundant 

 near the surface, and the greater the depth the more compact the soil and 

 the more difficult for the roots to penetrate. Hence it occurs that most 

 forest trees which start in life with strongly marked tap-roots have, at a 

 later period, lateral roots of a greater size than the main descending axis. 



In very many plants, instead of a single root growing downward from 



