CHAPTER II 



THE R( N >T 



18. Character of Primitive Plants. — The first forms of life 

 upon the earth were doubtless unattached unicellular plants that 

 lived in the water or nil list 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., wen 

 performed alike by each cell. This was easily accomplished owing 

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

 surrounded by water which contained all the substances required 

 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, ot 

 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 tin- absorption of materials became a necessity. Tins 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 rool 

 commands our attention because of its fitness For the accomplish- 

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



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

 onstruction of its f Is are absorbed by the roots: 



19. Root Hairs. We will first be interested to examine tin 

 structure and nature of the absorbing apparatus of the root. It' 

 seeds of radish, mustard, or other plant arc 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 



irered with delicate hairs ili.^. 29, A). There are several 

 interesting features about these rool hairs, in the first place the) 



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