CHAPTER VII. 



THE ROOT. 



74. Analogous members. — It has been pointed out that, 

 among the lower plants, there are very many which possess 

 structures similar in form and function to the root, and 

 sometimes called by the same name. Although these parts 

 serve to hold the plant in place, and perhaps to absorb 

 material from the substratum, they are not to be looked upon 

 as homologous with the roots of the higher plants, but as 

 merely analogous with them. In the plants whose vegetative 

 body is a thallus the gametophyte is the prominent phase. 

 In no case does the gametophyte produce true roots. It is 

 not until the sporophyte becomes an independent plant that 

 true roots are found in the vegetable kingdom. It is, there- 

 fore, only among fernworts and seed-plants that these organs 

 are to be found. When the sporophyte is developed as an 

 independent plant, it becomes necessary for it to produce 

 some organ capable of holding it in place, or of absorbing 

 materials from the outside, or of doing both. The organ 

 developed to meet this need is the root. 



75. Primary roots. — In accordance with their origin, 

 roots are either primary or secondary. Primary roots are 

 those which are developed directly from the egg from which 

 the entire plant takes its rise. The spherical egg in most 

 of the fernworts begins its development by a division into 

 hemispheres. The hemispheres divide into quadrants ; each 

 of the quadrant cells divides into two, forming octants of the 

 original egg. Division continues and the fundaments of 

 primary root, foot, stem, and one or more leaves appear 



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