LINUM USITATISSIMUM 



387 



phloem groups, and no central pith; but above this point, the 

 center of the axis is parenchymatous and there is a gradual reorien- 

 tation of the vascular elements. (Fig. 197, /I.) Each of the 

 phloem groups divides to form four phloem regions in the low^er 

 one-fourth of the hypocotyl; and, at a higher level, they become 



Fig. 197. A-D, transections of six-day seedling showing vascular transition : A, about 

 2. mm. below ground level ; B, middle hypocotyl showing parenchymatous pith and disin- 

 tegration of protoxylem ; C, upper region of hypocotyl showing eight metaxylem groups 

 with associated phloem ; D, at base of cotyledons and epicotyl showing vascular bundles 

 of cotyledon : a, b, bundles which anastomose to form double bundle of cotyledon ; a', b', 

 lateral bundles of cotyledon : en, endodermis ; mx, metaxylem ; pel, pericycle ; ph, phloem ; 

 fx, protoxylem; vb, vascular bundle of first foliage leaf. (After Crooks.) 



equally spaced at about 90° intervals from one another. (Fig. 

 197, B.) The primary phloem of the leaf traces of the first two 

 foliage leaves is dow^nwardly differentiated into the hypocotyl 

 and anastomoses with the phloem of the cotyledonary bundles at 

 about the point where the phloem groups of the lower hypocotyl 

 are branched. 



