Ch. V. 2] 



STRUCTURE OF R(JOTS 



215 



True soil roots are found onlj^ in the Flowering Plants and 

 Ferns. The lower land plants (the Bryophytes, or Moss 

 plants) have substitutes iji large hair-like ehizoids. The 

 Algae need no roots, since they absorb through their whole 

 bodies, though the Rockweeds have attachment organs, 

 somewhat like roots in aspect. In the Fungi no roots occur, 

 although their slender absorbing mycelial threads (page 84) 

 possess certain characteristics of root hairs. 



While soil roots are primarily organs of absorption and 

 anchorage, they also perform other functions, becoming 

 storage organs, spines, climbing organs, and even foliage, as 

 will presently be noted. 



2. The Structure of Roots 



The principal features of root structure can be seen very 

 well in the root system of some garden herb or house plant 

 carefully lifted and washed free 

 of adherent soil. Observation of 

 such material shows that the 

 entire root sj'stem of a plant is 

 continuous, without any trace of 

 such nodes as occur in the stem. 

 Each part is typically cylindrical, 

 though often forced by the soil to 

 other shapes. The branching is 

 very irregular, in marked con- 

 trast to the phjdlotactic sym- 

 metrj' of the shoot, but answering 

 to the composition of the soil ; 

 but in some seedlings the first side 



roots appear in vertical rows corresponcUng to the fibro- 

 vascular bundles which enter the roots from the stem, — e.g. 

 in Bean seedhngs four such rows occur. AH new branches of 

 roots originate deep in the tissues, in contact with the fitbro- 

 vascular bundles, whence they make their way out through 

 the overlying tissues, partly by the solvent action of diges- 



FiG. 158. — Cross section of 

 the fibrous part of a young root 

 of ii Bean, Phaseolus multijioriis. 

 (From Sachs.) 



