LINUM USITATISSIMUM 



385 



which differentiate stelar tissue in the same manner as occurs in the 

 primary root. (Fig. 196, D.) The stele is diarch and the primary 



Fig. 196. A-H, transections of young primary roots showing origin of lateral roots; a, 

 outer layer of first two layers derived from pericycle; a', outer layer derived from a; a", 

 inner layer derived from a; a" Qphni), periblem ; b, inner layer of first two layers derived 

 from pericycle; b' , outer layer derived from b; b" , inner layer derived from b; c, cortex; 

 cal, calyptrogen ; dgn, dermatogen ; e, endodermis ; hd, hypodermis ; pel, pericycle ; pi, 

 plerome; px, protoxylem. Derivatives of layer a' become calpytrogen and dermatogen; 

 those from layer a" become periblem ; and those from layer b, plerome. (After Crooks.) 



