6 BOTANICAL GAZETTE [july 



a rotation of the xylem, the protoxylem becoming exarch. On 

 reaching the transition region, near the base of the hypocotyl, the 

 phloem of each bundle divides, and passes to the right and left of 

 the xylem. Each half moves to the side of the stele, finally fusing 

 with a half of the phloem from the other bundle. This forms a 

 typical diarch root, the transition being that of Type III of Van 

 Teeghem. Fig. 17 shows a diagram of the path of the vascular 

 tissue at this stage. 



STAGE 11 



In the second stage, the first pair of leaves have enlarged 



sufficiently to be seen easily by the naked eye (fig. 19). The 

 primordia of the second pair of leaves are not differentiated until 

 near the end of this stage. The bases of the cotyledons have fused 

 to form a short tube. The leaves of the first pair are opposite and 

 are decussate to the cotyledons. As they develop, there begins the 

 differentiation of a single vascular bundle for each, the differen- 

 tiation beginning at the node, passing outward into the leaf, and 

 downward into the stem, passing through the very short epicotyl 

 into the hypocotyl, and becoming inserted between the cotyledonary 

 bundles, the protoxylems finally disappearing near the base of the 

 hypocotyl. 



There have also started to develop two buds, one axillary to 

 each cotyledon, but at this stage neither shows any differentiation 

 of vascular tissue. A diagram of the course of the vascular tissue 



this 



ermis are verv nearlv as in the 



stage, the angles of the outer cortical cells being more thickened, 

 however, and the outer wall of the epidermal cells being heavier 

 than before. Glandular hairs of the type found on the mature 

 plant (figs. 26 and 27) are numerous on the hypocotyl and 

 cotyledons. 



At the close of this period of development, a bundle develops 

 on each side of the stem between the two traces of the first pair of 

 leaves. These bundles, at the lower end, are forked just over the 

 cotyledonary traces, the forks being inserted on either side of the 

 traces, between them and the bundles from the first leaves. At 

 the upper end, the bundles fork, the branches Dassiner off nearly 



