THE WALLFLOWER 



79 



shape, and have distinct leaf -stalks ; their venation is 

 also different from that of ordinary leaves. The part 

 of the stem which comes below the cotyledons, i.e. 

 between them and the 

 tap-root, is called the 

 hypocotyledonary stem or 

 hypocotyl (hyp in Fig. 30). 

 It is in this region that 

 the transition between 

 stem and root structure 

 takes place. From each 

 cotyledon we can trace 

 two vascular bundles into 

 the hypocotyl. As soon 

 as they enter it they are 

 joined by the bundles of 

 the next leaves above ; but 

 with these we need not 

 concern ourselves, for only 

 the bundles of the coty- 

 ledons extend down into 

 the root. The hypocotyl, 

 therefore, contains four 

 vascular bundles only, two 

 on each side. Their posi- 

 tion is different from that 



FIG. 30. Wallflower seedling. 

 s, stem ; c, c, cotyledons, or 

 first leaves ; hyp, hypocotyle- 

 donary stem; G G, level of 

 ground ; r, root. Two-thirds 

 of natural size. (R. S.) 



of the ordinary vascular bundles of the stem. In each 

 pair the two protoxylem groups are not directed 

 straight inwards, but are turned towards each other, 

 and this is the case even at the point where they first 

 enter the hypocotyL The phloem groups are not 



