Internal Phloem in Gelsemium sempennrens, Ait. 49 



each other, thus, — < >— , but as the hypocotyl increases 

 in age, the cells of the arms move apart, taking a lateral posi- 

 tion, with the phloem external to them, usually two patches to 

 each side. This is illustrated in Plate IX, Fig. 4. 



As differentiation proceeds more spiral tracheae are inter- 

 polated between those already formed, so that a continuous 

 ring of protoxylem is finally present. The phloem consists 

 of small patches of finely divided cells, along the outer margin 

 of the sides of the wood, but is not yet continued around the 

 ends. At the level of the cotyledons, the phloem from the 

 sides bends toward the ends, and the zone is thus completed. 

 No recognizable internal phloem could be distinguished in the 

 young hypocotyl. 



In an older hypocotyl, in which secondary growth has 

 gone on for some time, the fundaments of two internal phloem 

 patches may be obser\^ed just below the cotyledonary node. 

 The round hypocotyl becomes elliptical, preparatory to the 

 separation of the cotyledons. Five or six large embryonic 

 cells appear on the inner side of the wood. Their nuclei are 

 large, and take a darker stain than the adjoining cells. In 

 short, the fundament of an internal phloem patch has arisen 

 in the leaf trace bundles, destined for the first, third, fifth and 

 succeeding pairs of leaves. No such fundament is demonstra- 

 ble in the pair of bundles for the cotyledons, second, fourth 

 and succeeding pairs of leaves. With increased age these 

 embryonic cells become a mass of small, finely divided cells, 

 so that evidently the bundles for the odd pairs of leaves each 

 possess an internal phloem patch. Throughout the lower 

 and middle portions of the epicotyl, or the internode above 

 the cotyledons, the opposite bundles are devoid of internal 

 phloem, but just below the node bearing the first pair of leaves, 

 two groups of embryonic cells appear in them, representing 

 the fundaments of the internal phloem patches for the even 

 pairs of leaves. When the node bearing the second pair of 

 leaves is reached, all four patches of internal phloem are 



4 



