8 Science of Plant Life 



may seem more akin to the stones among which it is rooted 

 than to the animals that live about it. But when we study 

 living beings, we find that there are activities other than 

 movement, such as respiration and growth, that are regularly 

 associated with life. As we shall see later, these processes 

 take place in plants the same as in animals and are evidence 

 that plants are as truly alive as are animals. 



A plant definitely related to its environment. The roots 

 of the ordinary green plant penetrate the soil in all directions 

 from the base of the plant, and enable it to take up water 

 and mineral substances. The stem commonly grows upward 

 and supports the leaves. Thus the leaves are displayed to 

 sunlight and are in contact with the oxygen needed for res- 

 piration and the carbon dioxid required for the making of 

 food. Each part of the plant is related to its environment in 

 such a way that its natural processes and the life of the plant 

 as a whole may be carried on. 



Mutual dependence of the parts of a plant. The roots, 

 stems, and leaves, together, make up the plant's machinery 

 of nutrition, and upon the efficiency with which the work of 

 each part is done depends the successful nourishment of the 

 plant. The chemical nature of the soil, the amount of water 

 it contains, and its other characteristics, may facilitate or 

 hinder the work of the roots. This may in turn aid or inter- 

 fere with the work of the leaves, and as a result the whole 

 plant may flourish or be dwarfed. Likewise, the leaves may 

 be exposed to favorable or unfavorable conditions of light 

 and moisture, and their work may be accelerated or 'retarded. 

 This in turn affects the stem and the roots, and the whole 

 plant shows its abundant nutrition or its lack of food. 



Under favorable conditions of light and moisture corn may 



