34 HOW PLANTS GROW. 



Section IV. — Different Forms or Kinds of Roots, Stems, and Leaves. 



81. The Organs of Vegetation, or those that have to do with the life and growth 

 of a plant, are only three. Root, Stem, and Leaf. And the plan upon which j^lants 

 are made is simple enough. So simple and so few are the kinds of parts that one 

 would hardly expect plants to exhibit the almost endless and ever-pleasing diver- 

 sity they do. This diversity is owing to the wonderful variety of forms under which, 

 without losing their proper nature, each of these three organs may appear. 



82. The study of the different shapes and appearances which the same organ 

 takes in different plants, or in different parts of the same plant, comparing them 

 with one another, is called MorpJwIogy, and is one of the most interesting parts of 

 Botany. But in this hook for vouno- beginners, we have onlv room to notice the 

 commonest forms, and those very briefly, — although sufficiently to enable stu- 

 dents to study all common plants and understand botanical descriptions. Those 

 who would learn more of the structure and morphology of plants should study the 

 Lessons in Botany. 



§1. Of Boots. 



83. The Root is the simplest and least diversified of the three organs. Yet it 

 exhibits some striking variations. 



84. As to origin, there is the primary or original root, fomied from the embryo 

 as it grows from the seed, and the branches it makes. Annuals, biennials, and 

 many trees are apt to have only such roots. But when any portion of their stems 

 is covered by the soil, it makes secondary roots. These are roots which spring 

 from the sides of the stem. Every one knows that most stems may be made to 

 strike root when so covered and having the darkness and moisture which are gen- 

 erally needful for roots. Perennial herbs and most shrubs strike root naturally in 

 this way under ground. All the roots of plants raised from tubers, rootstocks, and 

 the like (74-76), are of this sort, and also of plants raised from slips or cuttings. 

 In warm and damp climates there are likewise many 



85. Aerial Roots, namely, roots which strike from the stem in the open air. In 

 summer we often find them springing from the joints of the stalks of Indian Corn, 

 several inches above the soil. Some of these reach the ground, and help to feed 

 the plant. In the famous Banyan-tree of India aerial roots on a larger scale strike 

 from the spreading branches, high up in the air, grow down to the ground and into it, 



