/ 



ROOT DURATION 21 



In peat bogs the conditions for aeration seem to be particularly 

 bad. Such a place is i)ractically if not entirely undrained and the 

 de(>p layers of i)eat, constantly saturated with water, prevent the 

 entran(;e of oxygen and facilitate the accumulation of carbon diox- 

 ide. The acidity that results from this accumulation of carbon 

 dioxide brings about a condition of physiological dryness. Under 

 such conditions many plants which flourish in ordinary swamps 

 cannot grow at all. Many plants which are found in peat bogs have 

 structural features that are characteristic of dry land plants and 

 this has been attributed largely to the physiological dryness of the 

 bog. 



Another factor that prevents proper aeration of the soil, and so 

 reacts unfavorably on root growth is compactness. In national and 

 state parks many trees have been killed in picnic areas and camp 

 grounds as a result of numerous automobiles running over the soil 

 and compacting it to such an extent that neither w^ater nor air could 

 enter. Rainwater always contains a considerable amount of oxygen 

 in solution and one of the benefits of a rainstorm comes from the 

 oxygen that is carried into the soil but, if the soil is so compact, 

 that all of the w^ater flows away instead of percolating into the soil, 

 no aeration can result. One of the main reasons for preparing a 

 deep, mellow^ seed bed is to maintain a porous condition of the soil 

 in order that the roots may obtain sufficient oxygen for maximum 

 growi:h. 



10. Root Duration.— Some roots live for only a few weeks or 

 months while others, as those of some trees, may live for hundreds 

 of years. The classification of plants into annuals, biennials and 

 perennials is based largely upon the length of life of the parts within 

 the soil, though not in all cases on roots. An annual plant is one 

 that completes its life cycle within one vegetative season; a biennial 

 one that lives during part or all of two vegetative seasons; and a 

 perennial one that lives during more than two vegetative seasons. 

 In many biennial plants, such as the parsnip, practically the only 

 part that lives through the winter is the root. Many perennials, 

 also, are annual above ground and live through the winter below 

 ground. Some of these have perennial underground stems and in 

 these the roots may be, and often are, annual, while others have 

 perennial roots. Woody plants are perennial both above and below 

 the surface of the soil. 



Some plants may be annuals or biennials depending upon the 

 time of germination. Spring wheat, for example, is an annual while 



