PLATE 4° 
1. —Cross section of second (pathological) xylem-phloem cylinder in Plate 37, 
figure 2, showing in the center a ring of cambial cells surrounding other cells (phloem). 
Below are tracheae (T) some properly oriented, others lying at right angles to the 
long axis of the stem. The pith cavity lies in the direction of the arrow. X160. 
2. —Another swirl of cambium on the pith-cavity side of the second xylem-phloem 
ring in Ricinus communis . The xylem is in the lower part of the figure. X160. 
These cambial swirls appear to be concentric medullary bundles in the making 
Block 1265B. 
