34 HOW PLANTS GROW. 
Secrron 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 plants 
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 Morphology, and is one of the most interesting parts of 
Botany. But in this book for young beginners, we have only 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 Roots. 
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, formed 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, 
