PROBLEM A What Fart Do Roots and Stems Play in 



Making and Using Food? 



The plant underground. If we were 

 buried up to our waists, an observer 

 would get a false impression of us. But 

 that is the way you see most plants. Half 

 of the organism or more perhaps, is be- 

 neath the ground; the roots often spread 

 out as far as the stem with its branches. 

 The farther out or down the roots ex- 

 tend, the better they anchor the plant 

 in a storm and the more water they can 

 obtain. If you have growing bean plants, 

 uproot one and do Exercise i. 



Some plants have one long main root 

 corresponding to the main trunk of a 

 tree; this is called a taproot. (See Fig. 

 170.) The taproot may grow to a length 

 of twenty feet. It is more common for 

 plants to have many medium-sized roots 

 joined to the stem just below the surface 

 of the ground and branching in all 

 directions (Fig. 172). Just as a stem 

 branches into finer and finer twigs so 

 roots divide and subdivide into smaller 

 roots and rootlets. The finer rootlets 

 may be so small that one can scarcely 

 see them; the smallest twigs are thick 

 in comparison. The root systems of some 

 plants are astonishingly large. One biolo- 

 gist estimated that the total length of 

 the roots and rootlets of one rye plant 

 was two million feet; yet the plant was 

 only two feet high. 



Sometimes roots are thick and fleshy 

 and contain large amounts of sugar and 



starch. Man uses such roots as the car- 

 rot, sugar beet, turnip and sweet potato 

 as food. However, not every fleshy un- 

 derground part is a root. The Irish po- 

 tato and the onion, for example, are 

 stems, not roots. 



Roots above ground. Just as stems in 

 certain plants may be underground, so 

 may roots grow above ground. English 

 ivy, Boston ivy, and poison ivy have tiny 

 roots all along their climbing stems. 

 These roots cling to a stone or the bark 

 of a tree and support the plant. In the 

 jungle where the air is always moist 

 many kinds of orchid plants are perched 

 on the limbs of trees. They have roots 

 which hang down but never reach the 

 ground. 



Soil. You can learn a great deal about 

 soil at first hand by doing Exercises 2, 

 3, and 4. There are many different kinds 

 of soil. The soil of the forest floor is very 

 diff"erent from the soil at the edge of the 

 sandy beach. The black loam of Iowa 

 difl^ers from the red clay of New Mexico. 

 The soil in your back yard may not be 

 like any of them. But soil always contains 

 among other things small particles of 

 mineral compounds. Sometimes these are 

 very tiny, as in clay; sometimes they are 

 large, as in sandy soils. These mineral 

 compounds are nitrates, sulfates, phos- 

 phates, and man\' other compounds; no 

 two samples of soil taken from different 



