DEVELOPMENT BEHIND THE APEX 



323 



or just below the node of a leaf, in the largest central 

 bundle of the leaf trace, and the difierentiation of the 

 protoxylem progresses in both directions, downwards 



Fig. S3. — Diagrams of the differentiation of a stem behind the apex. 

 Qn the left is a diagram of a longitudinal section, on the right 

 of transverse sections at the levels A, B and C : I, leaf ; ax.bud., 

 axillary buds ; desm., desmogen strand ; px., protoxylem. For 

 further explanation see text. 



into the internode below and upwards into the leaf 

 (Fig. 53, px.). In other words, the elongated cells in a line 

 with the first formed spiral tracheids likewise become 

 converted into spiral tracheids, so that a strand of proto- 



