CHAPTER II 



THE ROOT 



1 8. Character of Primitive Plants. — The first forms of life 

 upon the earth were doubtless unattached unicellular plants that 

 lived in the water or moist places. All the varied functions of 

 the plant body, as the absorption of gases and material from 

 the soil and the manufacture of organic compounds, etc., were 

 performed alike by each cell. This was easily accomplished 

 owing to the simplicity of the organism and also because the plant 

 was surrounded by v/ater which contained all the substances re- 

 quired in the construction of foods. Perhaps the first change 

 produced in these plants by their surroundings was a modification 

 of a part of a cell so that it served as an organ of attachment, or 

 root, anchoring the plant to the substratum. As the plant con- 

 tinued to change and become more complex, and especially as it 

 became more and more subject to drier conditions, special organs 

 for the absorption of materials became a necessity. This change 

 from an aquatic to a terrestrial life finally left the root alone in 

 touch with the crude materials. Thus the root which at first was 

 only an anchoring organ, came later to function also as the prin- 

 cipal absorbing organ of the plant. Next to the leaf the root 

 commands our attention because of its fitness for the accomplish- 

 ment of this work. Practically all the water required by the 

 plants, and all the elements, save carbon and oxygen, utilized in 

 the construction of its foods are absorbed by the roots. 



19. Root Hairs. — We will first be interested to examine the 

 structure and nature of the absorbing apparatus of the root. If 

 seeds of rad^ish, mustard, or other plants are germinated upon 

 moist sand or moist blotting paper it will be seen when the roots 

 have attained a length of several cm. that a portion of each root 

 is covered with delicate hairs (Fig. 29, A). There are several 

 interesting features about these root hairs. In the first place they 



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